The seriousness of metabolic syndrome is not due to the disease itself but its promotion of other diseases, such as erectile dysfunction and cardiovascular and cerebrovascular diseases. We investigated the effects of Korean red ginseng (KRG, Panax ginseng) extract on erectile function in a rat model of metabolic syndrome. We divided the rats into three groups: control, metabolic syndrome+normal saline (N/S) and metabolic syndrome+KRG. To determine the occurrence of metabolic syndrome in all groups, body weight and various biochemical parameters (e.g., blood glucose, insulin, cholesterol) were measured, and the intra-abdominal glucose tolerance test was performed. To investigate penile erection, the peak intracavernosal pressure (ICP), mean arterial pressure (MAP) and Masson's trichrome stain were evaluated. Erectile function was also investigated by measuring the cyclic guanosine monophosphate (cGMP) levels of the corpus cavernosum. We found that the various biochemical parameters and body weight were similar in the metabolic syndrome+KRG group and the control group, although the values were slightly higher. The peak ICP/MAP ratio of the metabolic syndrome+N/S group was markedly decreased compared to the other groups. The cGMP level of the corpus cavernosum in the metabolic syndrome+N/S group was significantly lower than that of the other groups. As demonstrated in this model of metabolic syndrome with erectile dysfunction, KRG may improve erectile function.