Five species of marine cladocerans, Evadne nordmanni, Evadne tergestina, Podon leuckarti, Podon polyphemoides and Penilia avirostris, were found in Chinhae Bay during the years 1982-1983. Incidence of E. nordmanni(April-May) in spring and of E. tergestina(June-December), E. avirostris(June-November) in summer through autumn was noticed during the present study. But P. polyphem oides appeared throughout the year except February. P. avirostris was the most abundant species(21,491indiv./㎥), followed by P. polyphemoides and E. tergestina. Population of E.normanni and P. leuckarti was extremely poor and recorded to be less than 1,000indiv./㎥. Seasonal change in size composition was noticed in E. tergestina and P. avirostris. Increase of length was recorded in P. polyphemoides when water temperature lower than 15$^{circ}C$.