The 2003–04 UEFA Cup was won by Valencia in the final against Marseille.

It wrapped up a league and UEFA Cup double for Valencia.

The association ranking based on the UEFA country coefficients was used to determine the number of participating teams for each association:[1] Moreover, the following teams also qualified for the competition: For the 2003–04 UEFA Cup, the associations were allocated places according to their 2002 UEFA country coefficients, which took into account their performance in European competitions from 1997–98 to 2001–02.

[2] Apart from the allocation based on the country coefficients, associations could have additional teams participating in the UEFA Cup, as noted below: The following was the access list for this season.

[3] Due to the UEFA Cup title holder (Porto) qualifying for the Champions League via their domestic league, the following changes to the access list were made: Due to the suspension of Azerbaijan, the following changes to the access list were made: The labels in the parentheses show how each team qualified for the place of its starting round:[4] The schedule of the competition was as follows.