Phitsanulok (Thai: พิษณุโลก) is a provinces (changwat) of Thailand, located in the north. Neighboring provinces are (from east clockwise) Loei, Phetchabun, Phichit, Kamphaeng Phet, Sukhothai, Uttaradit. In the north-east it also has a short border with Xaignabouli of Laos.

The first element Phitsanu (Thai: พิษณุ) is a cognate of Vishnu, a Hindu god (see, e.g. Witsanu, Thai: วิษณุ). Lack of a v sound in the Thai language accounts for the two forms. The second element lok (Thai: โลก) means globe or world. A loose translation of the entire name would be Vishnu's Heaven.

Most of Phitsanulok has a hot tropical climate with considerable annual rainfall (annual rainfall is approximately 1.8 meters). In the higher altitude regions of the province, however, the climate is cool, with temperatures peaking at around 25° Celsius, sometimes dropping below the freezing point. With regard to rainfall, there is a dry season and a rainy season. The rainy season begins in the spring and ends around November. Deforestation and urban development along the river banks, combined with the extensive amount of rainfall in the region, have led to some climate change issues, primarily manifested in recent severe flooding within the province and elsewhere downstream of the Nan River.

Phitsanulok (Thai: พิษณุโลก, pronounced [pʰít.sa.nú.lôːk]) is an important and historic city in lower northern Thailand and is the capital of Phitsanulok Province, which stretches all the way to the Laotian border. Phitsanulok is one of the oldest cities in Thailand, founded over 600 years ago. It is probably best known as the birthplace of King Naresuan, who freed the country from Burmese domination in the late 16th century, and his brother and successor King Ekathosarot (Sanphet III). As the cross-road between the northern and central regions of the country, it has long been important both for political and strategic reasons, and was fought over many times in centuries past. Phitsanulok was the capital of Thailand for 25 years during the reign of King Boromma Trailokanat of Ayutthaya. Located on the banks of the Nan River, the city was originally a small Khmer outpost known as Song Kwae, before the Khwae Noi River changed its course in the 11th century AD. Phitsanulok was also a provincial center of the Angkorian Empire during the Angkorian period. Phitsanulok is home to Naresuan University and Pibulsongkram Rajabhat University, as well as to a major Royal Thai Army base.