PURPOSE: As the first-line pharmacotherapy for erectile dysfunction (ED), phosphodiesterase type 5 (PDE5) inhibitors are widely used and their clinical efficacy is well established. But up to now, most of these comparative studies have been based on questionnaires, and Udenafil and Mirodenafil, which have recently been developed in South Korea, have not yet to be compared in clinical studies. We compared and analyzed the efficacy of five PDE5 inhibitors using the sexual stimulated (SS)-Penogram. MATERIALS AND METHODS: A total of 347 patients taking PDE5 inhibitors for the treatment of ED and underwent SS-Penogram was enrolled in this study. AUC (area under the curve) of SS-Penogram was compared in each PDE5 inhibitors. Differences in AUC according to age, combined disorders, serum testostereone and prolactin, cholesterol and IIEF were also analysed using Chi-square and Kruskal-Wallis test. P-value less than 0.05 was considered as statistically insignificant. RESULTS: Ratios of Type I curves in medication groups with normal erection were not statistically different before and after medication. Ratios of the excellent response (>50 % increase in area under the curve) and non-response groups (no increase or even decrease in area under the curve) in each medication group were not statistically different. CONCLUSIONS: In this clinical comparative study of the efficacy of PDE5 inhibitors using the SS-Penogram, there were no definite differences in efficacy among PDE5 inhibitors.