A total of 16 teams competed in the league, with Muangthong United as the defending champions.

Therefore, at the end of season the three teams in the Thai Premier League that finished the season in the bottom three places (14th, 15th and 16th) would face the fourth, fifth and sixth teams from Division One in a promotion/relegation series.

Sriracha, Chula United and Nakhon Pathom were relegated to the 2010 Thai Division 1 League after finishing the 2009 season in the bottom three places.

The three relegated teams were replaced by 2009 Thai Division 1 League champions Police United, runners-up Royal Thai Army and third place Sisaket.

1 Second half of season played at Bangkok University Stadium[18] former home in Rangsit 2 Moved from Nong Chok Stadium during renovation 3 Ground share with Muangthong United during TOT Stadium Chaeng Watthana renovation 1 Nakhon Pathom were suspended for two years following the final playoff game, all results stood.