Phitsanulok (Thai: พิษณุโลก, pronounced [pʰít.sā.nú.lôːk]) is a city municipality in northern Thailand and the capital of Phitsanulok province. It had a city population of 60,827 and an urban population of approximately 200,000 in 2024, making it Thailand's 19th-most populous city proper and one of the major urban centers in the northern region. Located in the geographic center of the province, it occupies the fertile plains along the banks of the Nan River, which flows south to join the Chao Phraya River.

Phitsanulok was founded in the 11th century as a small Khmer outpost called Song Khwae (lit. 'two rivers'). The city served as the second capital of various kingdoms on several occasions; during the late Sukhothai Kingdom, and during the Ayutthaya Kingdom under King Borommatrailokanat, who resided in the city to defend against the Lanna Kingdom. He unified the western and eastern Song Khwae settlements and renamed them "Phitsanulok". Due to its strategic importance as Ayutthaya's northern outpost, the city frequently faced Burmese attacks. When war with the Konbaung dynasty led to Ayutthaya's collapse in 1767, Chaophraya Phitsanulok declared himself king and briefly established Phitsanulok as a capital before it was incorporated into the Thonburi Kingdom. The city maintained its significance throughout the subsequent Rattanakosin period.

Phitsanulok is considered one of the country's oldest cities and is home to Wat Phra Si Rattana Mahathat, which houses Phra Phuttha Chinnarat, one of the most famous and copied Buddha images in Thailand. The city serves as an educational hub, with Naresuan University being the main higher education institution in the lower northern Thailand. The city's location has made it a transportation hub, with comprehensive public transport services including city buses, a railway station on the Northern Line connecting Bangkok to Chiang Mai, and Phitsanulok Airport offering flights to Bangkok and serving surrounding provinces.

Phitsanulok is one of the oldest cities in Thailand, the site of "Muang Yommarat" (เมืองยมราช), a circular-moated Dvaravati settlement dating from the 6th to 10th centuries with a diameter of approximately 1 kilometer, founded 8 kilometers northwest of the present-day city center. The new city named "Song Khwae" was later founded over 600 years ago, located 5 kilometers south of the present-day Phitsanulok. According to the retrospective chronology derived from the textual evidence presented in the Ayutthaya Testimonies, the city of Phitsanulok was established in 937 by a monarch of Sankhaburi named Sudhammaraja. It then became under the Angkor influence around the 11th – 12th centuries.

Phitsanulok was originally named "Song Khwae" (lit. "Two Rivers") as it used to be situated between the Nan and Khwae Noi Rivers, although the Khwae Noi River now drains into the Nan River ten kilometers to the north of Phitsanulok. The Northern Chronicles credited the foundation of Song Khwae to "King Srithampidok" or King Thammaracha I of Sukhothai, on the east bank of Nan River. King Thammaracha I also constructed the Wat Phra Si Rattana Mahathat and cast famous Buddha images of Phra Buddha Chinnarat and Phra Buddha Chinnasri. Song Khwae eclipsed Sukhothai in importance, becoming the royal seat of Sukhothai Kingdom in 1378. After the demise of the last King of Sukhothai at Song Khwae in 1438, Prince Ramesuan of Ayutthaya came to rule Song Khwae. When Prince Ramesuan was crowned as King Trailokanat of Ayutthaya in 1448, Song Khwae and the Sukhothai Kingdom were incorporated into the Ayutthaya Kingdom.

During the Ayutthaya-Lanna War, King Trailokanat moved his residence to Song Khwae in 1464 and renamed the city "Phitsanulok" (from Sanskrit Vishnu and Loka "world"). He expanded the city westward to the west bank of Nan River. In the sixteenth century, Phitsanulok was the seat of Uparaja or heir presumptive to Ayutthaya throne who took residence in the Chantana Palace on the west bank. In 1548, King Maha Chakkraphat appointed his supporter Phra Pirenthorathep as "King Thammaracha" of Phitsanulok as a tributary ruler. During the Burmese-Siamese Wars, Phitsanulok and the Sukhothai region became battlegrounds between Burma and Siam. When King Bayinnaung invaded Phitsanulok in 1563, King Thammaracha of Phitsanulok submitted to the Burmese.

King Thammaracha, now reigned at Ayutthaya, appointed his son Prince Naresuan as the Uparaja of Phitsanulok in 1570. In 1584, Prince Naresuan ordered the evacuation of all cities in the Sukhothai region including Phitsanulok down south in preparations against Burmese invasions. Phitsanulok was abandoned until it was later restored in 1593 not as a Uparaja seat but as a Muang Ek or first-level city held by a governor, becoming the center of Siamese administrations in northern regions. The governors of Phitsanulok held the title "Chao Phraya Surasi". After the Second Fall of Ayutthaya in 1767, Phitsanulok came under the rule of Chao Phra Fang, a monk who declared himself a local lord based on the town of Fang (modern Uttaradit). King Taksin of Thonburi sent forces to capture Phitsanulok in 1768 and appointed Boonma (later Prince Maha Sura Singhanat) as Chao Phraya Surasi the governor of Phitsanulok.

The Burmese General Maha Thiha Thura laid siege on Phitsanulok in 1775. Chao Phraya Chakri (future King Rama I) and his brother Chao Phraya Surasi Boonma held the city for four months until the city finally fell to the Burmese. Phitsanulok was utterly destroyed on this occasion. The Burmese invaded again in 1785 and Phitsanulok was abandoned temporarily because the manpower shortage left the city defenseless. After the series of warfare, Phitsanulok was in ruins and depopulated through the nineteenth century. The Phra Buddha Chinnasri image was moved to Wat Baworn Niwet in Bangkok in 1829. In 1834, the Phuan people were deported from Muang Phuan in Laos to re-populate Phitsanulok and surrounding cities. Phitsanulok slowly recovered to be an urban center.