The 2006 Thai Premier League had 12 teams. No clubs would be relegated as the league would be expanded to 16 teams for the 2007 season. Two teams promoted from the rival Pro League and two clubs from Thailand Division 1 League. The official name of the league at this time was Thailand Premier League.
League champions and runners up Thailand Tobacco Monopoly and PEA should have taken part in the 2006 Asian Champions League, but both clubs failed to meet the respective time frame to send in squad lists. Both teams were duly disqualified from the competition. Rumor was rife that neither club wished to take part due to the financial costs.