In order to investigate the expression and roles of SelS in human umbilical vein endothelial cells (HUVECs, ECV₃₀₄ cells), total RNAs were extracted with TRIzol from adipose tissues of human, then the 1 102 bp fragment of SelS was amplified by RT-PCR. After the expected 1 102 bp PCR fragment was purified, SelS was cloned into pMD18-T vector. Purification, RT-PCR, restriction endonuclease analysis and DNA sequencing were performed to confirm the results. pMD18-SelS was incubated in presence of XhoⅠ/ClaⅠ and then ligated into pLNCX2 vector corresponding restriction sites. RT-PCR and DNA sequencing were performed to confirm a 1 102 bp SelS gene fragment was successfully inserted into pLNCX2. The ECV₃₀₄ cells were stably infected with pLNCX2-SelS or pLNCX2 alone and positive clone was obtained by G418 selection. After transient transfection, ECV₃₀₄ cells expressed pLNCX2 was verified by neo^r gene detection and the expression of recombinant SelS in the ECV₃₀₄ cells was 1.76-fold higher than the endogenous level by RT-PCR. After the cultured ECV₃₀₄ cells was treated with hydrogen peroxide (H₂O₂, 100, 200, 300, 400 μmol/L) for 24 h, cell viability was measured by MTT assay and the intracellular maleic dialdehyde(MDA)was detected by TBA method. The results showed that ECV₃₀₄ cells were injured by H₂O₂, overexpressing SelS increased the cell viability apparently and inhibited the production of MDA induced by H₂O₂. So overexpressing SelS protects ECV₃₀₄ cells from injuring by H₂O₂, and SelS may have the antioxidant protection effective on endothelial cells.