The feeding habits of the blackthroat seaperch Doederleinia berycoides were studied using 650 specimens collected in the Southern Sea of Korea, from January to December, 2005. The size (standard length, SL) of the specimens ranged from 6.3 to 35.2 cm. D. berycoides is a piscivore that consumes mainly teleosts such as Engraulis japonicus, Acropoma japonicum, and Myctophum nitidulum. Of the fish species Engraulis japonicus was the preferred prey. D. berycoides also eats small quantities of shrimps, amphipods, euphausiids, mysids, and crabs. D. berycoides showed ontogenetic changes in its feeding habits. Smaller individuals (5-10 cm SL) fed mainly on shrimp. The proportion of shrimp decreased with increasing fish size, and this decrease paralleled the increased consumption of fish. Fish accounted for almost all of the stomach contents of individuals larger than 15 cm SL. Cluster analysis based on the percentage dry weight (%DW) identified two size groups: group A (<15 cm SL) consumed primarily shrimp and fish; and group B (15< cm SL) preyed exclusively on fish. There was little seasonal change in the diet of D. berycoides, but shrimp constituted 41.8% of the summer diet in %W.