Objective To study the acute toxicity of slow-release (poly lactic-co-glycolic acid) PLGA-gemcitabine microsphere and gemcitabine on mice.Methods Up and down procedure (UDP) was used to determine the median lethal dose (LD50) of PLGA-gemcitabine microsphere and gemcitabine on mice respectively.Results The LD50 of PLGA-gemcitabine microsphere on mice was 256.30 mg/kg,gemcitabine was 8.91 mg/kg.The difference was 28.8 times.Conclusion PLGA-gemcitabine microsphere can markedly reduce the acute toxicity of gemcitabine.