Abstract: Spinosad was prepared into microsphere using polylactic acid (PLA) as coating material (wall material) by emulsion solvent evaporation method.The optimum prescription and process conditions were determined by investigating the effects of concentration of PLA and ratio of oil phase volume to water phase volume on quality of preparing spinosad microsphere.The result showed that D50,span,drug-loading rate,entrapment rate,drug yield of the spinosad microsphere is 12.73 μm,1.481 1,31%,100.2% and 89.4% respectively and this preparation process has a good repeatability.Spinosad microspheres were observed by scanning electron microscope (SEM),the result showed that the microspheres are round beads which have relatively smooth surfaces.The result of analyzing differential scanning calorimetry (DSC) confirms that spinosad and PLA had formed drug-loaded microphere indeed.The determination result of laboratory toxicity showed that the bioactivity of self-made 5% suspension agent of spinosad microspheres and 2.5% spinosad suspension agent sold in the market against 2nd-instar larvae of Plutella xylostella are almost the same,LC50 value was 0.40 and 0.38 μg/mL,respectively.