Spintor is a new insecticide from natural resource, the active ingredient is spinosyns A and D, which are secondary metabolites from the aerobic fermentation of Saccharopolyspora spinosa on nutrient media. Effect of Spintor treatment on the larval parasitoid Microplitis rufiventris Kok. was evaluated. Pre- and post-feeding of S. littoralis 2^nd instar larvae on castor leaves treated with different concentrations of Spintor had adverse effect on the development of the parasitoid immature stages. Prolongation of the development periods (egg- larval duration and pupal stage) and decreasing of adult longevity were recorded when concentrations of 0.188 and 0.125ml/L water were tested. At concentrations of 0.188, 0.125, 0.0625 and 0.0313ml/L percentages of immerged parasitoids were decreased. The combined effect of Spintor and parasitism led to an obvious increase in host mortality compared to the treatment with Spintor alone: 4-days Lc50 values for parasitized and unparasitized larvae were 0.194 and 0.239 ml/L respectively.