The event is usually held at the end of June or the beginning of July and prolong for 3 days. The whole event is called Bun Luang, part of a Buddhist merit-making holiday also known as Bun Phawet (assembly day).

The town’s residents invite protection from Phra U-pakut, the spirit of the Mun river. They then hold a series of games and take part in a procession wearing masks made of the sheaths or bottom part of thick palm leaf stems. Bamboo sticky rice steaming baskets are stitched onto the tops of the sheaths to make the top section of the mask. 

The origins of this part of the festival are traditionally ascribed to a story of the Vessantara Jataka in which the Buddha in one of his past lives as a prince made a long journey and was presumed dead. The celebrations on his return were so raucous as to wake the dead.

The three day of the event are held as follows:

• Day 1: the first day is called “Wan Ruan”. A ritual will be held to invite the spirit of the Mun River. Then they will celebrate a lot of games and wearing masks, which made of coconut leaves, rice, etc., with colorful clothes   
• Day 2: the second day is a rocket festival with many interesting activities such as costume and dance competitions, parades, etc.
• Day 3: on the final day, locals will listen to sermons from monks.

Nowadays, the Phi Ta Khon Festival is not only a cultural activity but also a nation traditional festival in Thailand.

According to bestpricetravel.com and Wikipedia