Cadmium is one of the most harmful environmental pollutants and has major toxicological effects on marine organisms. The present investigation was performed to study the effect of sublethal concentrations of cadmium on the filtration rate and siphon histology of the clam, Venerupis aurea. All applied concentrations of cadmium were found to inhibit the filtration rate of the investigated species. Histopathological studies revealed also that exposure to 300 ppb of cadmium induced severe effects on the siphonal wall of the clam, which ultimately reduce the filtration rate. Firstly, it reduces the efficiency of the straining tentacles in preventing the entrance of large particles into the mantle cavity; secondly, it leads to contraction and shortening of the siphon that resulted in shortening of gill axis and reduction of interfilamentar space. This will reduce the power and capacity of the filter pump. Other histopathological effects of cadmium on the siphon were increased mucous secretion and constriction of the lumen that may affect the flow of water into mantle cavity. Moreover, it leads to necrosis of the outer and inner epithelia, derangement of muscle fibers and enlargement of blood lacunae.