AIM: To evaluate the protective effect of luteolin on endothelial dysfunction induced by tert-butyl hydro-peroxide (t-BOOH). METHODS: We observed the effect of luteolin on t-BOOH-induced contractions in the aorta rings with or without endot helium, which were incubated with luteolin (10-6 to 10-4 mol/L) for 30 min before determining the concentration-response to t- BOOH. Cultured endothelial cell line (ECV304) was pretreated with different concentrations of luteolin (10-6 to 10-4 mol/L) for 30 min and then exposed to 10 -5 mol/L t-BOOH for 24 hours. Cell morphology was observed , and cell viability was determined by MTT assay. Meanwhile, RT-PCR was used to measure the expression of eNOS and COX-1. RESULTS: Increasing concentrations of t-BOOH produced concentration-dependent cont ractions in aorta rings isolated from rats, luteolin effectively attenuated the contraction in a concentration-dependent manner, and the relaxation response was greater in intact endothelium segments. In MTT and RT-PCR assays, luteolin effectively reduced the cytotoxicity of t-BOOH to endothelium cell and increased the expression of nitric oxide synthase (eNOS) mRNA, which was greatly down-regulated by t-BOOH. CONCLUSION: Luteolin effectively protects the endothelium from the impairment of oxidative stress, and the protection could be related to its negative modulation towards t-BOOH-induced contractions in the aorta.