Background: Men with diabetes mellitus frequently experience erectile dysfunction (ED). Objective: The purpose of this study is to determine whether or not 5 mg of tadalafil daily is effective in treating erectile dysfunction in men who are diabetic. Patients and methods: In this trial, 50 diabetic males with ED were given 5 mg of tadalafil once daily for 12 weeks. Using the International Index of Erectile Function (IIEF) and penis-specific Color Duplex Doppler Ultrasonography, researchers evaluated tadalafil's effects on erection quality and duration. Results: Age of 45 was the median, and the average body mass index was 30.3 kg/m², 54 % of them were smokers. We found statistical significant (p-value < 0.001) increased 12 weeks IIEF score (median = 18.5, IQR = 13 – 22) when compared baseline IIEF score (median = 12.4, IQR = 10 – 17). Our results showed statistical significant (p-value < 0.001) increased 12 weeks PSV (median = 36, IQR = 35 – 37) when compared with baseline PSV (median = 33, IQR = 30 – 35). Using multivariate logistic regression analysis, we demonstrated that smoking, BMI, dyslipidemia and bad glycemic control were predictive factors for ED severity. Conclusion: Taking 5 milligrams of tadalafil once a day may help diabetic men's erectile dysfunction.