The 2008 AFC Champions League knockout stage was played from 17 September to 12 November 2008.
A total of eight teams competed in the knockout stage to decide the champions of the 2008 AFC Champions League.
West Asia Zone had four teams qualified, East Asia Zone had three plus the title holders.
Urawa Red Diamonds won 4–3 on aggregate.
The first leg matches were played on 8 October, and the second leg matches were played on 22 October 2008.