AIM: To observe protective effects of taurine on reactive oxygen species generation induced by homocysteine in rat vascular smooth muscle cells (VSMC). METHODS: Rat VSMC was incubated with various concentrations of homocysteine and taurine. The lactate dehydrogenase (LDH) activity which released into culture medium was elevated as an indicator for VSMC injury. The reactive oxygen species (ROS) - hydrogen peroxide (H2O2) and superoxide anion (O2- )were measured with luminol or lucigenin chemiluminescences method, and the mitochondria Mn-superoxide dismutase (Mn-SOD) and catalase (CAT) were also measured in treated VSMC. RESULTS: LDH leakage from cultured VSMC treated with homocystenie, was increased (P＜0.01 vs control), and it was markedly inhibited when co-incubated with taurine (P＜0.01). Homocysteine induced H2O2 generation from VSMC in a concentration dependent manner (P＜0.01 vs control). However, taurine (5, 10, and 20 mmol/L) significantly antagonized 0.5 mmol/L homocysteine-induced H2O2 generation in VSMC in a concentration dependent manner (P＜0.01 vs homocysteine alone group), although taurine itself did not alter the H2O2 generation in VSMC (P＞0.05 vs control).In this study, the superoxide anion in VSMC was not detectable by chemiluminent method. In addition, treatment of VSMC with taurine increased mitochondria Mn-SOD and CAT activity in a concentration dependent manner (P＜0.05), but homocysteine decreased mitochondria Mn-SOD and CAT activity (P＜0.01 vs control). In addition,co-administration of taurine markedly ameliorated homocysteine-induced inhibition of Mn-SOD and CAT activity in VSMC (P＜0.01 vs homocysteine alone group). CONCLUSION: Taurine antagonized the effects of homocysteine on ROS generation and anti-oxidant enzyme activities in rat VSMC in vitro.