The year 2004 was the 4th year in the history of World Extreme Cagefighting, a mixed martial arts promotion based in the United States.

WEC 9: Cold Blooded[1] was an event held on January 16, 2004, at the Tachi Palace in Lemoore, California, United States.

WEC 10: Bragging Rights[2] was an event held on May 21, 2004, at the Tachi Palace in Lemoore, California, United States.

WEC 11: Evolution[3] was an event held on August 20, 2004, at the Tachi Palace in Lemoore, California, United States.

WEC 12: Halloween Fury 3[4] was an event held on October 21, 2004, at the Tachi Palace in Lemoore, California, United States.