Abstract: OBJECTIVE To study the changes of the acute toxicity and component in vitro and vivo of Stelleropsis tianschanica by pre and post processing. METHODS The mice were divided into crude drug group 1(60.6 g·kg^-1), crude drug group 2(75.75 g·kg^-1), crude drug group 3(90.9 g·kg^-1), crude drug group 4(106.05 g·kg^-1), crude drug group 5(121.1 g·kg^-1), processing group 1(58.6 g·kg^-1), processing group 2(73.25 g·kg^-1), processing group 3(87.9 g·kg^-1), processing group 4(102.55 g·kg^-1), processing group 5(117.2 g·kg^-1)(all calculated by crude drugs). Stelleropsis tianschanica crude drug and processed product extracts of different concentrations were administrated once, and observed continuously for 14 d. Acute toxicity reaction in mice and animals' death were recorded, and LD₅₀ was calculated. Analyzed the total ion current of Stelleropsis tianschanica crude drug, processed products and drug-containing serum based on UPLC-Q/TOF-MS, and compared the composition changes of each component. RESULTS The LD₅₀ of Stelleropsis tianschanica crude drug extract was 91.465 g·kg^-1, and the 95% confidence interval was 83.929-98.680 g·kg^-1. The LD₅₀ of Stelleropsis tianschanica processed product extract was 104.900 g·kg^-1, and the 95% confidence interval was 95.584-122.774 g·kg^-1(all based on crude drugs). Only a darkened liver was observed in the dissection of dead animals, while there was no obvious changes founded in other organs. After processing, the chromatographic peak area of the 7 components was reduced, and the 3 components do not appear. Compared with processed products, there were significantly more metabolic or migrating components in the medicated serum of crude drugs, and the chromatographic peak of the blood components of processed products was significantly smaller than that of crude drugs. CONCLUSION Processing can significantly reduce the acute toxicity of Stelleropsis tianschanica, and this effect is related to the reduction or elimination of some components of Stelleropsis tianschanica.