The species compositilln and seasonal dynamics (abundance) of zooplanktonrnin Lake Ziway (a tropical lake) was studied from f1arch 19,H to f1arc, h 19UB.rnBimonthly vertical haul zooplankton samples were taken from 3 stations (2rnstations in the limnetic zone and 1 in the littoral zone) using a 61[)Jillrnmesh net. The 1 imnet ic community was domi nated by eycl opoi d cupepods 'Ihil ernthe 1 ittoral community by the Hotifera. Ca 1 anoi d copepods andrnffarpacticoids did not appear in the samples collected. The Cyclopoid copepod species identified and counted in each samplernincluded f1icrocyclops vilricans and Nesocyclops ~equatorialis. 6frocyclopsrnspecies was found in only three of the sampling periods. Diaphanosomarnexcisum and Alona davidi constituted the cladoceran population of the lake.rnThe Rot ifera were domi nant in terms of thf? number of speci es. Out of thern13 species of Rotifera identified, the numerically dominant species wasrnBrachionus angularis and the least ilbundant species were ~. falcatus andrnLecana luna which were encountered in (lnly two and one sampling periodsrnrespect i ve ly. r~i nor groups of zooplankton recorded inc 1 uded Chi ronomi drnlarvae, the Ostracod Cypria javana, an unidentified nematod and anrnunidentified i1rthropod larva. 1111 major zooplankton groups and species identified shol'lcd significantrnseasonal variation in their abundance. Copepods and cladocerans both atrngroup and spec i es 1 eve 1 s hO~led max i mum abundance du ri n9 the I'let sea son and minimum abundance during t.he dry season. The Roti fera in general peakedrnafter the rainy season. t,1aximum contribution to the annual totalrnzoop 1 ankon abundance came from eyc 1 opoi d zoop 1 ankters. The abundancernpattern of the zooplankton of the lake are discussed in relation tornsuggested environmental factors.