Objective Karber’s method was applied to test the median lethal dose ( LD50 ) of Spiropreussione A in KM mice by intraperitoneal injection． Methods KM mice which half is male and another half is female were used to measure 100% lethal dose by Sequential method first，the rest was divided into 5 groups randomly． The ratio of high dose group and low dose group is set up as 1. 25 ( or 0. 8) ． Then the KM mice were administered Spiropreussione A at different dosages through intraperitoneal injection． Toxicity symptoms and times of death of the mice were recorded，and LD50 of Spiropreussione A on mice was calculated． Ｒesults Different degrees of peritoneal irritation were observed in each group and it was more significant in female than male． The peritoneal irritation disappeared after 30 min． The LD50 of Spiropreussione A was 5. 35mg /kg，95% confidence interval was ( 4. 69 ～ 6. 11) mg /kg． Conclusion This experiment showed that the LD50 of Spiropreussione A is 5. 35 mg /kg and the mortality is dose-dependent．