Objective. To characterize the time course of alterations in vasoconstrictor properties of arteries during simulated weightlessness, and to examine whether these alterations are reversible. Method. The tail-suspended rat model was used to simulate weightlessness, and the alterations in vasoconstrictor response were examined in vitro using isolated arterial rings. Result. Compared with that of controls, contractile tension evoked by KCl and phenylephrine (PE) were lower in abdominal aortic, mesenteric and femoral arterial rings from 2 wk tail-suspended rats (P<0.05); after 4 wk tail-suspension, the responses of mesenteric and femoral arterial rings to KCl or PE were further decreased (P<0.05); but contraction responses of arterial rings from 8 wk tail-suspended rats were similar to that of 4 wk simulated microgravity rats. The reversibility of altered arterial vasoreactivity after 4 wk tail-suspension was observed for 5 wk. Vasoreactivity of abdominal aortic rings was recovered after first week of recovery, but it took five weeks that altered vasoreactivity of mesenteric and femoral artery got back to normal. Conclusion. The alterations in constrictor properties of arteries are dependent on both the duration of tail-suspension and the position of artery, the diminished vasoconstrictor properties appear to reach a new steady state after 4 wk tail-suspension, and the changes are reversible.