The active substance cadmium chloride is highly toxic and showed damage to a multitude of non target species. The bivalves have been used for many years to determine the pollution status of water. In the present study static bioassays were performed on bivalve, Lamellidens marginalis to evaluate the median lethal concentrations of cadmium chloride (CdCl2) for 96 hrs. The LC50 values for 96 hrs were 3.5, 9.0 and 2.0 ppm, in summer, monsoon and winter respectively. The results showed that the LC50 values decreased with increase in exposure period.