The 2005 AFC Champions League was the 24th edition of the top-level Asian club football tournament and the 3rd edition under the current AFC Champions League title. The championship was retained by the Saudi Arabian club Al Ittihad with a 5-3 aggregate victory over UAE side Al Ain. Following a 1-1 draw at the Tahnon Bin Mohammed Stadium in Al Ain in the first leg, Ittihad recorded a 4-2 victory at the Prince Abdullah Al Faisal Stadium in Jeddah to lift the trophy for the second consecutive season.
A total of 28 clubs are divided into 7 groups of four, based on region i.e. East Asian and Southeast Asian clubs are drawn in Group E to F, while rest are grouped in Group A to D. Each club plays double round-robin (home and away) against fellow three group members, a total of 6 matches each. Clubs receive 3pts for a win, 1pt for a tie, 0pts for a loss. The clubs are ranked according to points and tie breakers are in following order:
Points earned between the clubs in question
Goal Differential between the clubs in question
Goal For between the clubs in question
Points earned within the group
Goal Differential within the group
Goal For within the group
The seven group winners along with the defending champions qualifies to the quarter-finals.
All 8 clubs are randomly matched; however, the only restriction is that the clubs from same country cannot face each other in the quarterfinals. The games are conducted in 2 legs, home and away, and the aggregates goals decides the match winner. If the aggregate goals cannot produce a winner, away goal rules in used. If still tied, clubs play extra time, where away goal rule still applies. If still tied, the game goes to penalties.