The 2003–04 Thai Premier League had 10 teams. Two clubs would be relegated and 2 teams promoted from Thailand Division 1 League. The team that finished in 8th position would play in a relegation play-off.
Again in another revamped and expanded Asian Champions League, last years runners up BEC Tero Sasana met their match and came bottom of a tough group comprising sides from China, South Korea and Japan. Krung Thai Bank also entered this year and came in second place in their group, although still not good enough to qualify for the knockout stages.