The concentrations of organophosphorous pesticides (OPs) were determined in the surface water of Asan Bay, Korea in May and August 2005. During this period, the highest concentrations of OPs measured in the surface water were 2816.9 ng l-1 for IBP and 485.3 ng l-1 for DDVP. The concentrations of chlorfenvinfos and azynfos-ethyl were relatively high ranging ND~185.9 ng l-1 and ND~169.2 l-1 respectively. Diazinon, disulfoton, methidation, malathion, parathion, azynfos-methyl were also frequently detected in the surface water of Asan Bay with concentrations generally lower than 100 ng l-1. The concentrations of IBP, diazinon, parathion, chlorfenvinfos, azynfos-ethyl were fairly high in August than in May. The concentration of organophosphorous pesticides generally decreased with increasing distance from the shore implying progressive dilution in the marine environment. OPs adsorbed on suspended particles were also studied. DDVP, phorate, stirofos, EPN, azinphos-methyl and IBP had higher adsorption capacity onto suspended particles than other pesticides.