2003–04 LEN Euroleague
The 2003–04 LEN Euroleague is the 41st edition of LEN's premier competition for men's water polo clubs. It ran from 17 September 2003 to 29 May 2004, and it is contested by 38 teams. The Final Four took place on May 28 and May 29 in Budapest.
Preliminary round
| Key to colors in group tables |
| Group winners and runners-up advanced to the [|Quarter-finals] |
Group A
Group B
Group C
Group D
Knockout stage
Quarter-finals
The first legs were played on 14 April, and the second legs were played on 28 April 2004.Final Four ([Budapest])
, Budapest, HungaryFinal standings
| Team | |
 Honvéd | |
 Jadran Herceg Novi | |
 Primorje | |
 Šturm 2002 |