To investigate the effect of corosolic acid treatment on erectile function in metabolic syndrome induced rat model. Fifty male 3-week-old SD rats were fed a high fat and high sugar diet. Six months later, metabolic variables were determined. Metabolic syndrome induced erectile function (MED) rats were confirmed by an apomorphine test. Then MED rats were treated with corosolic acid daily by oral gavage for 4 weeks. To evaluate erectile function, intracavernosal pressure (ICP)/mean arterial blood pressure (MAP) ratio was measured. Thiobarbituric acid reactive substances assay and dihydroethidium staining were used to assess reactive oxygen species (ROS) level. Protein expressions of gp91phox and eNOS were examined by western blotting and immunohistochemistry. Fasting blood glucose, body weight, total cholesterol and insulin were markedly increased in metabolic syndrome rats compared with those of the control rats (p < 0.05). The ratios of max ICP/MAP and area under curve (AUC)/MAP was markedly reduced in MED rats compared with the control rats (p < 0.05). The concentration of cyclic guanosine mono-phosphate (cGMP) and the expression of eNOS were significantly decreased in MED rats compared with the control group (p < 0.05). Moreover, ROS level and the expression of gp91phox were significantly increased in MED rats. Treatment with corosolic acid reversed these changes (each p < 0.05). Corosolic acid reduces the level of ROS, ameliorating endothelial dysfunction and improvement of erectile function in MED rats.