Lectins are glycoproteins that specifically bind carbohydrate structures and may participate in the biodefense mechanisms of fish. In this study, the binding of three lectins, Dolichos biflorus agglutinin (DBA), soybean agglutinin (SBA), Bandeiraea simplicifolia BS-1 (isolectin B4), Triticum vulgaris (WGA), Arachis hypogaea (PNA) and Ulex europaeus (UEA-I) were studied in the gill, liver, intestine, kidney, heart, and spleen of the flat fish Paralichthys olivaceus. DBA was detected in intestinal mucous cells, as well as in gill epithelial and mucous cells. It was weakly detected in renal tubule epithelial cells and in bile duct epithelial cells. The strong SBA staining was seen in the intestinal club cells, in bile duct epithelial cells and renal tubule epithelial cells. There were intense positive reactions for isolectin B4 in gill epithelial and mucous cells, and the strong isolectin B4 staining was seen in epithelial cells of the bile duct and intestine. The strong WGA staining was seen in the gill mucosal cells, sinusoid, renal tubule epithelial cells and mucosal cells of the intestine. UEA-I was detected in the gill epithelial and mucosal cells, bile duct epithelial cells and renal tubular epithelial cells. These results suggest that the six lectins examined were localized in the covering epithelia of the various organs of the flat fish and they may participate in the biodefense mechanism of the intra body surface in which is exposed to various antigens.