Phase Two of the Tet Offensive of 1968 (also known as the May Offensive, Little Tet, and Mini-Tet) was launched by the People's Army of Vietnam (PAVN) and Viet Cong (VC) against targets throughout South Vietnam, including Saigon from 29 April to 30 May 1968. The May Offensive was comparable in bloodshed to the initial phase of the Tet Offensive. The United States (US) had 2,169 men killed by hostile action in the month of May, making it the deadliest month of the entire Vietnam War for US forces, but South Vietnamese losses were 3,467, significantly less than the 5,025 killed in February during the original Tet Offensive. The US claim that PAVN/VC losses exceeded 24,000 killed and over 2,000 captured. The May Offensive was a costly defeat for the PAVN/VC.

In late March 1968, COSVN and B2 Front leaders held meetings to review the results of the Tet Offensive. Lê Duẩn, the driving force behind the Tet Offensive, and General Hoàng Văn Thái wished to renew the offensive before the start of the southern monsoon began in mid-May in order to improve their position at the Paris Peace Talks which were about to commence. Some field commanders opposed any renewed offensive citing the heavy losses suffered by the VC and resulting poor morale, the inexperience of replacement PAVN troops and logistics problems, while Allied post-Tet operations Truong Cong Dinh and Quyet Thang meant that "there was no longer any opportunity to liberate the cities and province capitals" with a Tet-style offensive. COSVN leaders ignored these objections believing that the element of surprise meant they still had the advantage over Allied forces and recommended to the Politburo that the offensive should be renewed. After consulting with the other fronts in South Vietnam, the Politburo instructed the PAVN high command to begin planning the new offensive. Part of the offensive was meant to "bring the war to the enemy's own lair", meaning to shift the battlefield from the countryside to significant urban attacks, with the resulting damage inflicted upon urban centres. The targets of the attack was more limited than the Tet Offensive, but still primarily aimed at attacks throughout Saigon and major urban centres.

Unlike the original Tet Offensive which sought to seize nearly every major city in South Vietnam in the hope of provoking a general uprising among the population, the new offensive only involved an assault on Saigon with other towns and cities being harassed by mortars, rockets and artillery fire. Approximately 60,000 PAVN/VC soldiers would take part in the offensive including 30 PAVN infantry regiments, four artillery regiments, three composite PAVN/VC infantry regiments and ten VC provincial infantry battalions. The major targets would be Saigon and Đông Hà near the Vietnamese Demilitarized Zone (DMZ). Regimental-strength operations were planned in Bình Định and Kon Tum Provinces.

On 19 April, the PAVN chief political officer of Sub-Region 1, Lieutenant colonel Tran Van Dac, surrendered to South Vietnamese forces in Bình Dương Province. Dac revealed that the PAVN/VC planned to attack Saigon and other targets across the country at the end of April. After two days of questioning, US and South Vietnamese intelligence concluded that Dac was telling the truth and his information and other signals and human intelligence led COMUSMACV General William Westmoreland to advise his senior commanders that another offensive was imminent and instruct them to move forces back to defend Saigon. News of Dac's defection leaked within days and the Politburo decided to proceed with the offensive given that Dac's knowledge was limited to the planned attacks on Saigon, but to delay the start of the offensive by one week, other than around the DMZ, in the hope that the Allies would think the Saigon attack had been cancelled and lower their guard.

On 29 April, the PAVN 320th Division attacked An Binh, north of Đông Hà Combat Base, this drew two Battalions of the Army of the Republic of Vietnam (ARVN) 2nd Regiment into a running battle and the 1st Battalion 9th Marines was sent in to support the ARVN resulting in a seven-hour long battle that left 11 Marines, 17 ARVN and over 150 PAVN dead. The following day the 3rd Battalion 9th Marines arrived to support the Marine/ARVN force and was ambushed north of Cam Vu, 20 Marines and 41 PAVN were killed. Also on 30 April, a PAVN unit opened fire on a US Navy Clearwater patrol from entrenched positions near Dai Do, 2.5 km northeast of Đông Hà. It was later discovered that four PAVN Battalions including two from the 48th and 52nd Regiments of the 320th Division had established themselves at Dai Do. The Battle of Dai Do lasted until 3 May and resulted in 81 Marines and over 600 PAVN killed. The PAVN engaged US and ARVN forces elsewhere around Đông Hà from 4–6 May, on the evening of 6 May the 2nd Brigade 1st Cavalry Division was deployed into Tru Kinh to conduct Operation Concordia Square and on 9 May was ambushed by a PAVN force resulting in 16 US dead for the loss of 80 PAVN. On 10 May a night attack north of Nhi Ha was broken up by air, artillery and naval support, 159 PAVN were killed. After this the 320th had broken into small groups and was moving back towards the DMZ, from 9–17 May the 2nd Brigade reported killing 349 PAVN for the loss of 28 killed.

While it seemed that the 320th had abandoned their attempts to take Đông Hà, this was just a temporary lull. On 22 May a unit from the 320th ran into a Company from 3rd Battalion 3rd Marines between Con Thien and Gio Linh and was caught in the open by Marine artillery and air support. East of Con Thien the 1st Battalion 4th Marines encountered another PAVN unit setting off a two-day battle as the PAVN tried to escape back through the DMZ resulting in 23 Marines and 225 PAVN killed. On 25 May in actions at Dai Do and Nhi Ha 350 PAVN were killed. In two actions at Tru Kinh on 26 May over 56 PAVN were killed for the loss of ten Marines, while the ARVN killed 110 PAVN north of Thuong Nghia. On 27 May the Marines killed 28 PAVN and by 30 May the 320th was attempting to escape through the Marine and ARVN cordon. Total PAVN losses in the second Battle of Đông Hà were over 1,000 killed.

At 04:00 on 5 May, a VC unit attacked ARVN positions at the Newport Bridge and simultaneously VC wearing Marine uniforms attacked Marine positions closer to the city centre. At 04:30 a battalion sized VC force was engaged near the Phú Thọ Racetrack where heavy fighting had taken place during the Tet Offensive. At 10:00 the ARVN Airborne was engaged by VC north of Tan Son Nhut Air Base. Two battalions of the VC 271st Regiment followed by another regiment, attacked eastward in the ARVN 5th Ranger Group's Cholon sector. Using small arms, automatic weapons, and rocket fire, they attempted to seize the headquarters of the 6th Police Precinct. Throughout the morning, the 30th Ranger Battalion was heavily engaged with forces of the 3rd Battalion, 271st Regiment, less than 3 km due west of the Phú Thọ Racetrack. Although the Rangers had managed to slow the VC with artillery and helicopter assistance, the fight was still raging in the early afternoon. UH-1 Huey helicopter gunships of the 120th Aviation Company Gunship Platoon at Tan Son Nhut AB were called in to support the Rangers and they hit the VC positions, one gunship was hit by VC fire and crash-landed and burnt on the ground while the crew escaped unharmed.

On 6 May, the 3rd Squadron, 4th Cavalry Regiment was engaged by a VC force near the village of Ap Hoa Thanh on the western edge of Saigon. The ARVN 30th and 33rd Ranger Battalions joined with US Cavalry forces to attack a hamlet west of Phú Thọ Racetrack, meeting heavy resistance they withdrew and called in air and artillery strikes, on entering the hamlet the next morning they counted over 200 VC dead. A unit from the 199th Light Infantry Brigade was engaged by VC forces in a hamlet west of Saigon starting a three-day running battle, after multiple air and artillery strikes the US force overran the village, finding concrete-reinforced bunkers which had only been destroyed by delayed-fuze 750 lb bombs.