A 3 × 2 factorial experiment was conducted to investigate the proper dietary protein and lipid levels for growth of subadult olive flounder reared in suboptimal water temperature. Six diets were formulated to contain three levels of protein (40, 45, and 50%) and two levels of lipid (7 and 14%). Triplicate groups of fish (initial body weight of 255 g) were hand‐fed to apparent satiation for 14 wk in suboptimal water temperature (15.5 ± 1.3 C). The highest weight gain and feed efficiency were observed in fish fed the 45 and 50% protein diets with 14% lipid. Protein efficiency ratio, daily feed intake, condition factor, and hepatosomatic index of fish fed the 14% lipid diets were significantly or slightly higher than those fed the 7% lipid diets at the same protein level. Crude lipid contents of the liver and viscera of fish fed the 14% lipid diets were significantly higher than those fed the 7% lipid diets at the same protein level. The results of this study suggest that at 15 C an increase of dietary lipid level from 7 to 14% can improve growth and protein utilization irrespective of protein levels (40, 45, and 50%), and the diet containing 45% protein and 14% lipid would be suitable for optimal growth and effective protein utilization of subadult olive flounder when reared at 15 C.