Abstract: Chemical molluscicides are useful in schistosomiasis control. A synergistcan potentiate the efficacy and reduce the dosage of a molluscicide, thus decreasing thetoxicity and environmental pollution. In order to search for potential molluscicidalsynergists, 13 compounds of O, O - dialkyl- O - (2-substituted- 3-benzofurylacetonitrile-α-oximino)phosphate or thiophosphate (VI_1～13) and 2 compounds of O, O - dialkyl-O-(2-thienylacetonitrile-α-oximino)phosphate(X_14.15)were prepared. Preliminary testdemonstrated that compound X₁₅ had strong synergic effect with sodium pentachlorophenolin combating mollusks. Compounds X₁₄ and VI_{1.2.3.6.8.10.12. 13.} also showed some molluscicidalsynergistic activity.