This study involves an investigation on the effects of a pesticide, metal and a detergent as individual and mixtures on esterase and antioxidant enzyme activity of the freshwater snail Helisoma duryi. Adult snails were exposed to sublethal concentrations of copper (5 µg/L), industrial detergent, oxyfoam (15 µg/L), carbaryl (25 µg/L) as well as mixtures of these pollutants for 96 hours. Carboxylesterase and cholinesterase activities were measured using 4-nitrophenyl acetate and acetylthiocholine iodide as substrates respectively. The activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione S-transferase were also measured as indices of oxidative stress. Esterase activity was inhibited in snails exposed to carbaryl, copper or detergent. Mixtures of the different chemicals also caused inhibitions of esterase activity when compared to the controls. All the chemicals individually and as mixtures, caused enhanced activities of antioxidant enzymes. When comparing all the antioxidant enzymes analyzed, the highest activity was caused by the triple mixture of the pollutants. The results suggest that aquatic life is at risk to adverse effects of pollutant mixture as reflected by increased alteration of enzyme activity in mixture-exposed snails though the increase was less than sum of effects of individual pollutants. More studies on the effects of a wider range of pollutant mixtures on aquatic organisms are needed however, for the full appreciation of reactive interactions that takes place in complex mixtures which ultimately affect the health of aquatic biota.