The present study deals with the bioconversion of desmosterol to cholesterol in the prawn, Penaeus japonicus. After administration of desmosterol-26-^{14}C, the bioconversion products were investigated by using thin-layer and silver nitrate-impregnated silicic acid column chromatographies. As a bioconversion product, cholesterol-^{14}C was identified. These results suggested that the prawn, P.japonicus possesses the enzyme systems for conversion of desmosterol to cholesterol.