Objective To compare the differences of dose-effect relationship in the toxicity qualitative response between the ultrafine powder and coarse powder of strychni semen on mice.Methods The acute toxicity test and 7-day repeated dose toxicity test were used.The dose-effect and time-effect of ultrafine powder on the qualitative response of strychni semen were observed according to the mortality rate

median lethal dose（LD50）

minimum lethal dose（MLDLD1）and maximum tolerated dose（MTDLD0）.Results The LD50

MLDLD1and MTDLD0of strychni semen ultrafine powder on male mice was 194.7mg/kg

100mg/kg and 85mg/kg respectively and on female mice was 163.0mg/kg

85mg/kg and 70mg/kg respectively.The LD50

MLDLD1and MTDLD0of strychni semen coarse powder on male mice was 295.7mg/kg

115mg/kg and 100mg/kg respectivelyand on female mice was 271.8mg/kg

100mg/kg and 85mg/kg respectively.As the dose increased

the death latency of mice induced by strychni semen ultrafine powder was shortened more quickly than coarse powder.Conclusion The toxicity response of strychni semen ultrafine powder and coarse powder is similar in mice.The acute toxicity has a time-effect relationship with dosedependence.The micronization can increase the acute toxicity and repeated dose toxicity in the lethal qualitative response.