The event has attracted more than 100 boxers, including 66 males, representing18 teams from many provinces, cities and ministries across the country.
The athletes will compete in a total of 16 weight categories, including 10 for women.
The festival is scheduled to end on May 31.
Muay, known as Muay Boran, is a traditional martial art of Thailand. The 239-year-old sport has developed across the world and been competed in many international tournaments.