Investigation on species composition and abundance of zooplankton in Abak River, southeastern Nigeria was carried out for 12 months using filtration method. The result revealed that there were 5 taxonomic groups of zooplankton (namely: Cladocera, Copepoda, Nematoda, Polychaeta and Rotifera), comprising 81 cells/l, 13 species and 12 genera. The most abundant species was Polychaete larvae with 24 cells/l (29.63%) whereas Alonella dadyi, Alona rectangula and Temora longicornis recorded the least (1 cell/l; 1.23%). In terms of number of species, the most abundant zooplankton was the group Cladocera with 7 species (53.86 %) whereas the least were Nematoda and Polychaeta with only one species (7.69%); represented in the following descending order: Cladocera > Rotifera and Copepoda > Polychaeta and Nematoda. However, in terms of number of cells per litre, Cladocera also had the highest number of cells (29 cells/l; 35.81%) while the lowest number was observed in Copepoda with 3 cells/l (3.70%); group contributions in descending order were as follow: Cladocera > Polychaeta > Rotifera > Nematoda > Copepoda. Low species composition and abundance of zooplankton observed in this study can be attributed to the anthropogenic perturbations on-going in and around the Abak River.