Abstract: To study the tissue distribution of Loureirin B, an active ingredient of traditional Chinese medicine-dragons blood, and the potential effects of long-term simulated microgravity effect on drug distribution. SD rats were randomly divided into normal gravity group and simulated microgravity group. And rats were tail-suspended for 21 days to simulate microgravity effect. Single dose of 25 mg/kg Loureirin B was orally administered to all rats respectively. Heart, liver, spleen, lung, kidney, stomach, intestine, brain, testis and skeleton muscle samples were collected at 1 h postdosing. Concentration of Loureirin B in samples was determined by HPLC-MS/MS method to observe the effect of simulated microgravity effect on Loureirin B distribution in vivo. The results show that, Loureirin B is distributed significantly in the liver and stomach, followed by kidney, intestine, heart, spleen, skeletal muscle, lungand brain. The least distribution is found in brain. Compared with the normal gravity group, Loureirin B in the liver from the simulated microgravity rats is obviously increased by 47.7% (p<0.05), and the content of Loureirin B in rat brain is increased by 5.4-fold (p<0.05).Loureirin B is decreased significantly in the intestine and kidney with a decrease by 52.7% and 22.0% respectively (p<0.05).There is no dramatic difference in Loureirin B level of stomach, heart, lung, spleen, testis and skeletal muscle. Loureirin B distribution shows obvious tissue specificity. Loureirin B distribution in liver, intestine, brain and kidney of rats is evidently changed by long-term simulated microgravity effect.