The 2003/04 UEFA Champions League was the 12th season of the most important European competition for club teams in football under this name and the 49th overall.
As in the previous season, 72 clubs from 48 national associations took part in the competition, as Azerbaijan again did not have a representative. The season began on July 16, 2003 with the first qualifying round and ended on May 26, 2004 with the final in the Arena AufSchalke in Gelsenkirchen, which FC Porto won 3-0 against AS Monaco. It was the second time after the final in the Johan Cruyff Arena in 1997/98 that the final of the Champions League took place in a stadium with a closable roof.
According to the UEFA five-year standings , three teams from Italy (including defending champions AC Milan) were seeded for the group stage and one started in the third qualifying round. Two teams each were seeded from Spain and England; two more started in the third qualifying round. Two teams from Germany, France and Greece (places 4-6 in the UEFA five-year ranking) were also seeded for the group stage, but only one team each started in the third qualifying round. A team from the Netherlands, Portugal and Turkey (places 7–9) was selected for the group stage and one each started in the third qualifying round. Belgium, Austria, Russia, Scotland, the Czech Republic and the Ukraine (places 10–15) each sent one team to the 2nd and one team each to the 3rd qualifying round.
This year there were again changes in the game mode. The second group phase was canceled, but the first and second in each group qualified for the new round of 16. Another new feature was that the losers in the third qualifying round were allowed to continue playing for the first time in the first round of the 2003/04 UEFA Cup and were therefore not eliminated from the European Cup. The group third continued to play in the third round of the 2003/04 UEFA Cup . In the group stage, if two teams were tied, the following applies:
20 national champions, whose countries were placed under 28th place in the 2002 UEFA ranking , were drawn here and played one home and one away game against each other. The respective winners advanced to the second qualifying round.
The first leg took place on July 16, the second leg on July 23, 2003.
The 10 winners of the first qualifying round, 12 champions of European leagues who were placed between 17th and 28th place on the 2002 UEFA ranking list and 6 teams placed second in the leagues between 10th and 15th were drawn. The teams again played 2 games against each other and the winner advanced to the next qualifying round.
The first leg took place on July 30, 2003, the second leg on August 6, 2003.
The 14 winners from the second qualifying round, 7 champions from European leagues placed between 10th and 16th places on the 2002 UEFA ranking list, 3 second-placed teams from countries in 7-9 places, 5 third-placed teams from countries 1– 6 - since the Italian third place in the table AC Milan was also the defending champion from the 2002/03 season, the club moved directly into the subsequent group phase - and 3 fourth-placed teams from countries 1–3 were drawn here and played 2 games against each other. The winners advanced to the group stage and the losers progressed to the 2003/04 UEFA Cup first round .
The first leg took place on August 13, 2003, the second leg on August 27, 2003.
The 16 winners of the third qualifying round were drawn together with the champions of the 9 highest-ranking national associations and the second-placed clubs from countries 1 to 6 in the UEFA five-year ranking and the defending champion in 8 groups of 4 teams each. The two best clubs from each group advanced to the round of 16, while the third-placed teams continued to play in the third round of the UEFA Cup . The last in the group was eliminated from the European competitions.
FC Porto (2nd title)
Fernando Morientes (9)
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Bohemians Dublin
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SK Tirana
KR Reykjavík
Riga discount
FC Flora Tallinn
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Ertis Pavlodar
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FBK Kaunas
Barry Town United
FK Leotar Trebinje
HJK Helsinki
CSKA Sofia
Slavia Prague
Graz AK
Shakhtar Donetsk
Celtic Glasgow
RSC Anderlecht
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Djurgårdens IF
Maccabi Tel Aviv
Dinamo Zagreb
Rosenborg Trondheim
Ajax Amsterdam
Chelsea FC
Olympique Marseille
Borussia Dortmund
AEK Athens
1-0 Carlos Alberto (39th) 
Nuno Valente, Carlos Alberto, Jorge Costa
Walter Pandiani
Benni McCarthy
Didier Drogba
Juninho
