The present study was conducted to determine the safe and toxic levels of dietary copper in juvenile olive flounder, Paralichthys olivaceus, fed Mintrex® copper, a chelated dietary copper source. Fish averaging 3.8 ± 0.13 g (mean ± SD) were fed 1 of 10 diets (n = 3) containing 7 (Cu0), 10.4 (CuM5), 15.8 (CuM10), 24.9 (CuM20), 43.4 (CuM40), 82.1 (CuM80), 158 (CuM160), 308 (CuM320), 658 (CuM640), and 1267 (CuM1280) mg Cu/kg diet. At the end of 12 wk of feeding trial, weight gain (WG), specific growth rate, and protein efficiency ratio of fish fed CuM5 and CuM10 diets were significantly higher than those fed CuM80, CuM160, CuM320, CuM640, and CuM1280 diets (P < 0.05). Survival of fish fed Cu0, CuM5, CuM10, CuM20, and CuM40 diets was significantly higher than those of fish fed CuM320, CuM640, and CuM1280 diets. Whole-body lipid content of fish decreased while whole-body ash increased with dietary copper levels. Whole-body and tissue copper concentrations increased with dietary copper levels. Although ANOVA test suggested that the toxic level of dietary Cu in juvenile olive flounder, P. olivaceus, could be 320 mg/kg diet, broken-line analysis of WG indicated a level of 286 mg/kg diet when Mintrex®Cu is used as the dietary copper source.