Dejagah, 28, made 49 appearances during his two seasons at Fulham, scoring six goals, and leaves after the west London club were relegated from the Premier League last season.
"Having spoken with Ashkan, we decided in the best interest of both Fulham and himself, that he would leave," Fulham manager Felix Magath told the club's official website.
"During his time with us he made some good appearances and scored some memorable goals. However, we have decided to part ways.
"It will always be our policy to have players who are committed to the club and have a desire to work for the common goal."
Dejagah was a member of Iran's World Cup squad and appeared in all three of their group-stage matches, notably impressing in their 1-0 loss to Argentina.
- Sports & Recreation
- Ashkan Dejagah