〔Abstract〕 Objective To investigate the effect and mechanism of L-cysteine(L-cys) increasing endogenous H2S on hypertension induced by intermittent hypoxia in rats. Methods Male Sprague-Dawley rats were randomly divided into normal oxygen(Control) group, chronic intermittent hypoxia(CIH) group, Control+L-cys group and CIH+L-cys group. The rats in CIH group and CIH +L-cys group were exposed to 15 d intermittent hypoxia, 8 h daily. In L-cys treatment group, the rats were given L-cys(10 mg/kg)each day by the oral administration. Noninvasive measurement of tail artery systolic blood pressure(SBP) was measured by the tail cuff system. The renal sympathetic nerve activity(RSNA) renal sympathetic nerve activity(RSNA) were recordedin vivoon a PowerLab data acquisition system. The plasma concentrations of norepinephrine(NE) and H2S, activity of cystahionine-β-synthase(CBS) and cystahionine-γ-lyase(CSE) were measured by ELISA kits. Results Systolic blood pressure of tail artery significantly increased after CIH exposure, but did not change after normoxia exposure. RSNA and plasma concentrations of NE were also significantly higher in CIH rats than in control rats. The plasma level of H2S in CIH rats were significantly decreased than those in control rats.L-cys increased the level of H2S of CIH rats, and significantly inhibited the increase of blood pressure and excessive activation of sympathetic nerve activity induced by intermittent hypoxia. Conclusion L-cys can improve intermittent hypoxia induced-hypertension in rats by increasing endogenous H2S.