Zooplankton communities of the River Ossiomo at Ologbo, Niger Delta, Nigeria were investigated from April 2012 to December 2012. Three stations were studied from upstream to downstream with a distance of about 2 kilometres between each station. A total of 42 taxa were identified; 11 species of cladocerans, 6 copepods and 5 rotifers in the following order of dominance: copepoda > cladocera > rotifera. A total zooplankton population of 1330 individuals was recorded during the study period. Copepods and cladocera represented the predominant species (51.1% and 43.6% of the total zooplankton community respectively) followed by rofiters (5.3%). Copepods and cladocerans were dominated by both cyclopoid (51.1%) and chydorids (27.8%), respectively. The dominant copepod and cladocera species were Thermocyclops neglectus and Alona eximia representing 33.1% and 15.8% of the total zooplankton, respectively. The calculated diversity indices indicated that station 1 was more diverse followed by station 3, while zooplankton species in station 2 were least diverse. Community composition was similar at both stations 2 and 3, but varies seasonally across the three stations. Higher species number and density was found during the wet season with a trend of declining proportion towards the dry months.