The aim of this study was to investigate the effect of malachite green on the post-exposure filtration rate of Blood Clam, Barbatia virescens. Blood Clams were collected from the rocky coast and acclimated to laboratory conditions for 18 days. Bioassays were conducted wherein Blood Clams were exposed for 24 h to a clean medium (no malachite green), 0.06 mg l^-1 malachite green, 0.32 mg l^-1 malachite green, 5.06 mg l^-1 malachite green, and then to the same concentrations for 48 h. Filtration rate in all concentrations and malachite green-exposure durations were determined at 0.5, 1, 2, 3, 4, and 6 h. Blood Clams exposed for 24 h and 48 h to 0.32 and 5.06 mg l^-1 had significantly lower filtration rates than the control (p<0.05). Similarly, those exposed to 0.06 mg l^-1 for 48 h showed significant reduction in their filtration rates. The lower rate was associated with longer exposure to malachite green. In addition, Blood Clams exposed for 48 h were not able to improve their filtration rate, although they were transferred to a clean medium for 6 h. The green colouration on Blood Clams' muscles was also not eliminated. These findings suggest the ecological risk of malachite green to bivalves and its implications to the health of sessile coastal organisms.