Abstract: Based on biodegradable polylactic acid (PLA) as wall materials and emamectin benzoate as core materials,the sustained-release microspheres of emamectin benzoate were studied by using solvent evaporation method.The effects of reaction temperature,the ratio between core material and wall materials (emamectin benzoate weight/PLA weight,CP value) and the concentration of PLA on the particle diameter,surface morphology,drug-loading rate and entrapment rate of microsphere were investigated.The results showed that when the condition of the concentration of PLA and the ratio between core material and wall materials was fixed,the particle diameter,drug-loading rate and entrapment rate of microsphere achieved the best at 20 ℃.The particle diameter,drug-loading rate and entrapment rate of microsphere increased with the addition of concentration of PLA.With the change of the ratio of core materials and wall materials from 1∶1 to 1∶5,the particle diameter and drug-loading rate reduced gradually,but the entrapment rate of microsphere increased with the reduce of ratio of core materials and wall materials between 1∶1 and 1∶4.The entrapment rate of microsphere achieved the maximum 97.8% at CP value(1∶4).The smooth and complete microsphere of emamection-benzoate was formed when the CP value was between 1∶3 and 1∶5.The differential scanning calorimetry(DSC) determination demonstrated that emamectin benzoate and PLA were combined well to form the microsphere.The releasing curves of drug showed the emamection-benzoate microspheres had obvious slow-release efficiency.