Many organochlorine pesticides are persistent in the environment and have a tendency to bioaccumulate significantly through food chains. Aquatic environments are particularly more affected because the pesticides applied to agriculture systems are eventually carried into water bodies, through surface runoff, rivers, and groundwater flow. The objective of this paper is to study the effect of the coexistence of a heavy metal on the solubility enhancement of the two representative organochlorine pesticides, lindane and dieldrin, by humic acids. The solubility enhancement of pesticides by humic acid in a single system was compared with that in a binary system. The extent of solubility enhancement of lindane by humic acids was constant. while that of dieldrin by humic acids increased. Also, the solubility enhancement of dieldrin by humic acid with Pb decreased than that by humic acid without Pb.