The Battle of Masaka (Kiswahili: Mapigano ya Masaka) was a battle of the Uganda–Tanzania War that took place on 23 and 24 February 1979 in the town of Masaka, Uganda. Following artillery bombardment, most of the Ugandan government forces fled and Tanzanian and Ugandan rebel forces captured the town.

Colonel Idi Amin had seized power in a military coup in Uganda in 1971 and established a brutal dictatorship. Seven years later he attempted to invade Tanzania to the south. Ugandan troops occupied the Kagera Salient and subsequently murdered local civilians and destroyed property. The attack was eventually repulsed, and Tanzanian President Julius Nyerere, unsatisfied with Amin's refusal to renounce his claims to Tanzanian territory and the international community's failure to strongly condemn the invasion, ordered his forces to advance into southern Uganda with the aim of capturing the towns of Masaka and Mbarara.

After careful planning, the Tanzania People's Defence Force (TPDF) crossed the border in January 1979 and moved steadily northward. Masaka was garrisoned by several thousand Ugandan troops, including the Suicide Battalion. Their performance was undermined by low morale and internal divisions. The TPDF surrounded the town on three sides and on 23 February, after beating off several harassing Ugandan probes, initiated an artillery barrage, concentrating on the Suicide Battalion's barracks. Several Ugandan units withdrew to Lukaya, leaving the Suicide Battalion alone to defend Masaka. The TPDF's 201st and 208th Brigades attacked at dawn. A battalion of Ugandan rebels and the 207th Brigade—bolstered by a tank squadron—also moved in on the town. The Suicide Battalion withdrew towards the village of Villa Maria, and, aside from opposition at Kasijagirwa camp, the TPDF seized the town with minimal resistance. As revenge for the damage wrought by the Ugandans in Kagera, the TPDF razed much of Masaka. The loss of the town greatly hurt the morale of the Ugandan forces and troubled Ugandan commanders. Amin ordered a counter-attack which was defeated in Lukaya. His promise to exact revenge on the local civilians for welcoming the invasion partly contributed to Nyerere's decision to attack Kampala. Much of Masaka was later rebuilt.

In 1971 Colonel Idi Amin launched a military coup that overthrew the President of Uganda, Milton Obote, precipitating a deterioration of relations with the neighbouring state of Tanzania. Amin installed himself as president and ruled the country under a repressive dictatorship. In October 1978 he launched an invasion of Tanzania. On 1 November he announced the annexation of the Kagera Salient, an 1800 square kilometre (1118.5 square mile) strip of land between the Ugandan border and the Kagera River. Ugandan troops subsequently pillaged the area they occupied, murdering civilians, stealing cattle, and destroying property, triggering the flight of 40,000 inhabitants southward. Tanzania eventually halted the assault, mobilised anti-Amin opposition groups, and launched a counter-offensive. In January 1979 the Tanzania People's Defence Force (TPDF) seized the Ugandan border town of Mutukula to counter any further threats to Kagera. The TPDF bulldozed homes in the locale and murdered local civilians to avenge the destruction in Kagera. Deeply disturbed by the event, Nyerere subsequently instructed his troops to refrain from harming civilian life and property.

Though many international actors were sympathetic with the Tanzanian position, numerous African states and the Organisation of African Unity (OAU) strongly encouraged Tanzanian President Julius Nyerere to exercise restraint and not act beyond defending his territory. He had originally not intended to expand the war, but with Amin refusing to renounce his claims to Tanzanian territory and the OAU's criticism of the Kagera invasion being muted, he decided that Tanzanian forces should occupy southern Uganda.

The two major towns in southern Uganda were Masaka and Mbarara. The former was the third largest inhabited place in the country and the site of the southern headquarters for the Uganda Army. The Tanzanians decided to seize them as revenge for the devastation wrought by Ugandan troops in their country and in order to incite a rebellion. Obote assured Nyerere that if the locales were taken a mass uprising would take place against Amin's regime, deposing it in a few weeks and allowing the Tanzanians to exit the war. Obote was also certain (and Nyerere was partly convinced) that the Uganda Army would disintegrate if Masaka were captured. The Tanzanians began careful planning for an offensive on the two towns. Major General David Musuguri was appointed commander of the TPDF's 20th Division and tasked with overseeing the advance into Uganda. It was originally hoped that the Ugandan rebels could spearhead the attack, but there were only about 1,000 of them, so the Tanzanians had to lead the operation. Between the TPDF's positions and Masaka was a series of locations occupied by Ugandan troops that needed to be cleared out, including an airstrip and various artillery batteries. The 201st, 207th, and 208th Brigades were ordered to clear the way. They steadily advanced, killing dozens of Ugandan soldiers, destroying large amounts of their materiel, and seizing the airstrip on 13 February.

Meanwhile, Amin claimed that Tanzanian forces and mercenaries had seized a large portion of Ugandan territory. Facing questions from the international community, Tanzania insisted that its troops had only occupied land just over the Ugandan border. Tanzanian diplomats repeated Nyerere's proclamation that "Tanzania does not desire an inch of Ugandan territory" but evaded more specific questions about their troops' movements. After 24 Tanzanians were killed in an ambush at Lake Nakivale, the TPDF slowed its offensive. They dislodged the garrison of Kalisizo, a town 28 kilometres (17 mi) south of Masaka, inflicting heavy casualties. The Ugandans that retreated to Masaka were in a panicked state and demoralised the troops stationed there. Anticipating conflict, most of the civilian population, including the mayor, fled the town. The civilians mostly left out of fear of Masaka's garrison, as the Ugandan military was notorious for harassing civilians. At the recommendation of an Indian diplomat, the municipality's South Asian community evacuated.

Tanzanian commanders formulated their final plan of attack for Masaka after seizing Kiziba. The exact strength of Masaka's garrison was unknown to the Tanzanians, but it was assumed at the time to number in the thousands. The garrison was commanded by Brigadier Isaac Maliyamungu and included the Suicide Battalion, regarded as one of the best units in the Uganda Army. Nevertheless, the Ugandan military in general was lacking in discipline and was affected by internal divisions, reducing its combat effectiveness at Masaka. Lieutenant Colonel Bernard Rwehururu, the commander of the Suicide Battalion, suspected that after Kalisizo's fall Masaka would be attacked. He called a meeting with his fellow officers to discuss defensive strategy. Agreeing that the town should not be abandoned, the commanders drew up plans that called for troops to occupy specific locations. The Suicide Battalion was to defend Masaka from the Mutukula, Mbarara, and Bukakata–Nyendo roads and also guard the hill with the local television mast. Soldiers of the Chui Battalion and the First Infantry Brigade were allocated to the Kitovu and Buwala hills. According to journalist Faustin Mugabe, the Masaka garrison also included police officers who had been drafted into the Uganda Army.