Abstract: Objective: To study the effect and mechanism of sulodexide (SDX) on the oxidative stress and apoptosis of cardiac microvascular endothelial cells (CMEC) in rats under high glucose (HG). Methods: CMEC of rats were isolated and cultured, and randomly divided into control group, HG group and HG+SDX group. Cell survival rates were measured by cell counting kit-8 (CCK-8) assay. DCFH-DA was used as a fluorescence probe to determine the fluorescence intensity of DCF in each group to determine the level of intracellular reactive oxygen species (ROS). The activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) in the supernatant were compared. The apoptosis rate was detected by flow cytometry and TUNEL assay. The expression of AMPK, phosphorylated (p-) AMPK and SIRT1 proteins was detected by western blotting. Results: Compared with the control group, the HG group showed decreased cell survival rate, increased cell supernatant level of MDA, reduced SOD activity, elevated ROS level, increased apoptosis rate, and decreased expression of pAMPK、SIRT1 proteins (all P＜0.05). Compared with the HG group, the survival rate of CMEC cells in the HG+ SDX was significantly increased, the production of MDA and ROS was decreased, the activity of SOD was increased, the apoptosis rate of CMEC was decreased, and the expression of p-AMPK and SIRT1 proteins was significantly increased (all P＜0.05). Conclusion: SDX may alleviate HG-induced oxidative stress and apoptosis of CMEC by activating AMPK/SIRT1 signaling pathway, thus playing a cardiovascular protective role.