The present study was conducted to investigate the effects of Chlorella powder (CHP) as a feed additive on growth performance in juvenile Korean rockfish, Sebastes schlegeli (Hilgendorf). Six experimental diets were supplemented with Chlorella powder (CHP) at 0, 0.5, 1.0, 1.5, 2.0 and 4.0% (CHP0, CHP0.5, CHP1.0, CHP1.5, CHP2.0 and CHP4.0, respectively) of diet as a dry matter basis. Three replicate groups of fish averaging 2.1 ± 0.02 g (mean ± SD) were fed one of six experimental diets for 12 weeks. After the feeding trial, fish fed CHP0.5 had a higher weight gain and specific growth rate than did fish fed CHP0, CHP1.5, CHP2.0 and CHP4.0. However, there was no significant difference among fish fed CHP0.5 and CHP1.0. Fish fed CHP0.5 had a significantly higher feed efficiency ratio and a protein efficiency ratio than did fish fed the other diets. Fish fed CHP4.0 had a lower significantly serum total lipid than did fish fed CHP0, CHP0.5 and CHP1.0, however, there was no significant difference among fish fed CHP1.5, CHP2.0 and CHP4.0. Fish fed CHP2.0 had significantly higher serum albumin and lower serum glucose than did fish fed CHP0. Fish fed CHP4.0 had significantly higher liver protein and lower liver fat than did fish fed the other diets. These results suggest that the optimum dietary CHP supplementation level could be approximately 0.5% of diet for positive effects on growth and feed utilization without any negative effects on blood parameters and body composition in juvenile Korean rockfish.