The 2009–10 LEN Euroleague was the 47th edition of Europe's premier club water polo competition.

The Euroleague is run in five phases: [1] Seeded countries The eight countries with the best placed team in the preliminary rounds, or main group stage, in the previous year's competition, 2008–09 LEN Euroleague are seeded for this year's competition.

Each seeded country earns 1 place in the main group stage, 1 place in the second qualifying round, and 1 place in the first qualifying round.

These countries are: Unseeded countries All other countries were invited to enter up to two clubs into the first qualifying round.

The first legs were played on 24 March, and the second legs were played on 14 April 2010.