Purpose: To explore the protective effects of statin on irradiated human umbilical vein endothelial cells (VEC) and the thrombomodulin (TM) expression.Materials and Methods: Cultured VEC were treated by atorvastatin at a final concentration of 10 μ mol/ml for 10 minutes, and then irradiated at a dose of 2 Gy or 25 Gy.Twenty-four hours after irradiation, apoptosis of VEC was monitored by flow cytometry, and the expression of TM and protein C activation in VEC was assessed by flow cytometry and spectrophotometry, respectively.Results: After treatment by atorvastatin for 24 h, VEC assumed shuttle, triangular, or irregular shapes.There were many pseudopodia around the cells and more intercellular gaps, indicating that cells were in a relative active state of motion.When compared with VEC which had only been irradiated, pseudopodia were more obvious, but with less pyknotic and necrotic cells than VEC which had been irradiated and treated with atorvastatin.After treatment with atorvastatin for 24 h, the rate of cell apoptosis decreased by 6% and 16% in cells irradiated with 2 Gy and 25 Gy, respectively.TM expression increased by 77%, 59%,and 61% in untreated cells, 2 Gy irradiation-treated cells, and 25 Gy irradiation-treated cells, respectively.The protein C levels in 2 Gy and 25 Gy irradiation-treated cells was reduced by 23% and 34% when compared with untreated cells, but up-regulated by 79% and 76% when compared with cells which were irradiated and treated with atorvastatin.Conclusions: Statin can effectively prevent the γ-ray irradiation damage to VEC.This protective function is related to changing VEC cycle distribution by statins and strengthening its TM expression and protein C activating capacity.At the same time, it prompts that statins may have effective effects in protection of irradiation damage and healing of radioactive injury wound.