To investigate the residue of organophosphorus pesticides such as Monocrotophos[Dirnethyl-1-methyl-2-methyl carbamoylvinylphosphate] and EPN[O-ethyl-O-4-nitrophenyl phenylphosphonothioate] in the coastal environment of Cheju island. samples of sea organism. water and sediment were collected at the Sackdaldong and Daepodong near the Jungmoon golf course in July and Aug, 1997. The qualified detection limit of monocrotophos and EPN by GC-FPD were 0.024 ng/g and 0.020 ng/g in the sea organism, respectively. Neither Monocrotophos nor EPN was detected in seaweed cava (Ecklania cava), Agar (Gelidium amansii), turban sell (Batillus cornutus) and sea urehin (Anthocidaris Crassispina). They were not detected in seawater and sediment, either. These results showed that the coastal area near the Jungmoon golf course in the Cheju island was not polluted by the organophosphorus pesticides such as Monocrotophos and EPN.