The 1998 Thai Premier League consisted of 12 teams. The bottom club would be relegated to the Thailand Division 1 League. The club that came 11th would play in a relegation / promotion match against the club that came second in the Thailand Division 1 League Defending Champions Royal Thai Air Force should have entered the next edition of the Asian Club Championship, but refused due to lack of funding. BEC Tero Sasana took their place. The league was also known as the Caltex Premier League.