Buddhist Lent Day, also known as Khao Phansa Day, is an important holiday observed in Thailand. It takes place on the first day after the full moon of the eighth lunar month, marking the beginning of the three-month annual retreat observed by Theravada monks and devotees. During this time, most monks remain within their temples for meditation and study, refraining from traveling or visiting their families.

Khao Phansa Day is significant in Thai culture where Buddhism is the prevailing religion. On this day, Thai people make merit by offering food, candles and other necessities to the monks at their local temples. One highlights of this holiday is the 'lantern parade' and 'candle festival' in Ubon Ratchathani where intricately carved beeswax candles are paraded through the city.

Buddhist Lent Day is primarily a time for the Buddhist community to concentrate on meditation and spiritual cultivation, it also ushers in a time of sobriety and reflection for the greater Thai population. Many Thais use this period to give up vices or bad habits. In respect for this tradition, the sale of alcohol is banned in local stores on the Buddhist Lent Day. Whether one is a practicing Buddhist or not, everyone respects this day in Thailand.