Effects of Polygonum equisetiforme extracts against dichlorvos were investigated in the commercial clam Ruditapes decussatus. The toxicity of this pesticide was firstly tested in R. decussatus gill and digestive gland tissues using five doses varying from 0.05 to 1mg/l during 2, 4, and 7days. Results showed that 0.05mg/l of DDVP induced oxidative stress and neurotoxicity in R. decussatus after 2days of exposure. Investigations of the effects of P. equisetiforme extracts in R. decussatus exposed to 0.25mg/l of DDVP were made in clams receiving three concentrations (0.009, 0.045, and 0.09g/l) during 4 and 7days. Antioxidant enzymes SOD and CAT as well as H2O2 content and AChE were quantified by colorimetric method. Fourdays of exposure to DDVP increased SOD and CAT activities and enhances H2O2 content. AChE levels decreased considerably following DDVP exposure, although a restoration in the enzyme activity was observed with P. equisetiforme extract (E3 = 0.09g/l). Overall, P. equisetiforme extract at concentration (E1 = 0.009g/l) prevents oxidative stress caused by DDVP, while 0.09g/l of P. equisetiforme extract induced an effect similar to that obtained with DDVP alone. Nevertheless, this concentration was found effective for the restoration of the AChE activity.