Wadi El Rayan Lakes lie in Wadi El Rayan Depression, southwest of Cairo in the western desert of Egypt. Zooplankton samples were collected monthly during twelve cruises from February 1996 to January 1997. Crustacea constituted 70% of the total zooplankton organisms which were represented by Cladocera, Copepoda, and Ostracoda (27.74%, 7L79%, and 0.47% respectively).The Cladocera was represented by nine species dominated by Diaphanosoma excisum, though all of the cladoceran species were previously reported from Wadi El Rayan Lakes except Macrothrix laticomis. The Copepoda was represented by five species where Thermocyclops neglectus was the most dominating one (60% of total adult copepods). The Ostracoda was represented by only Cyprideis torosa. The first lake harboured the maximum numbers of Crustacea whereas their lowest numbers were recorded at the drain and the second lake. The peak of crustacean flourishing was during autumn.