This study was conducted to evaluate extruded pellet (EP) diet compared with a raw fish moist pellet (MP) diet for flounder, Paralichthys olivaceus on field feeding experiments in Jeju area. The experimental EP diet (juvenile, growing and adult) was prepared based on the former studies on nutrient requirements and feed ingredient of flounder. Fish were distributed randomly to each aquarium as a group of 102,300 fish (initial mean weight 97 g) in field experiment I and reared randomly to each aquarium as a group of 40,000 fish (initial mean weight 120 g) in field experiment II. In field feeding experiment I conducted in commercial flounder farm, survival, wt. gain (94-1,090 g), feed efficiency and condition factor of fish fed experimental EP were comparable to those of fish fed MP, but considerably higher protein efficiency ratio were observed in fish fed experimental EP. In field feeding experiment II, no significant difference was observed in final mean weight of fish fed the experimental EP (1,234 g) and MP (1,286 g), and any noticeable problem caused by feeding the experimental EP was not found during the whole period of feeding trial. Survival of fish fed the experimental EP was lower than that of MP, and there was no significant difference in feed efficiency between the fish fed experimental EP and MP. Therefore, these results strongly suggest that diet EP could be developed to replace MP diet for the marketable size (1.3 kg) of production for flounder without adverse effects on growth performance. In particular, abdominal dropsy and reduction of condition factor, which are frequently occurred in commercial EP feeding farms, were not observed in flounder fed experimental EP.