Objective:To observe the dynamic change of cystathionine β-synthase during cerebral ischemia-reperfusion and its effect in rats.Methods:The ischemic model was established with line embolism to block the middle cerebral artery .The reverse tran-scription-polymerase chain reaction ( RT-PCR) and Western blot assay were used to assess the expression of cystathionine β-synthase (CBS) in SHAM group,I group,and IR group.ELISA assay was performed to detected the homocysteine (HCY) level in plasma.After treating with the inhibitor of cystathionine β-synthase called hydroxyla mine(HA),the expression of hemeoxygenase 1(HO-1) and the pathologic change of the brain was evaluated .Results:As compared to sham group ,the expression of CBS was significantly up-regulated in ischemia-reperfusion group at 12 h post-reperfusion.Meanwhile,it existed the lowest level of HCY at 12 h post-reperfusion,comparing to sham grouzp ( 5.73 ±1.17 vs 2.88 ±0.93 , F=25.56 , P=0.001 ) .When inhibited the activity of CBS via using HA , the down-regulation of HO-1 protein and further damage in neuron were observed .Conclusion:Cystathionine β-synthase serves as an protective factor during cerebral ischemia-reperfusion.