Abstract: To study pharmacokinetics and excretion difference of loureirin B (LB) in rats after single oral administration between simulated weightlessness and gravitation condition, a series of test was executed. Rats were tail-suspended for 21 days to simulate weightlessness effect. After a single oral administration of 25 mg/kg LB, venous blood and excretion samples were collected at different time points. Concentration of LB in samples was determined by HPLC-MS method. Pharmacokinetic parameters and excretion amount were calculated. Results show that, compared with normal gravity rats, the area under cuve (<i<AUC</i<<sub<0-<i<t</i<</sub<), maximum concentration (<i<C</i<<sub<max</sub<), time to peak concentration (<i<t</i<<sub<max</sub<), volume of distribution (<i<V</i<<sub<d</sub<), elimination rate constant (<i<K</i<<sub<e</sub<), and biological half-life (<i<T</i<<sub<1/2</sub<) of simulated weightless rats ware significantly changed. Meanwhile, the excretion of LB in urine, feces, and bile are also up-regulated in simulated weightlessness group, while no obvious differences are observed.