ABSTRACT Introduction Tadalafil (a PDE5 inhibitor) is used to treat erectile dysfunction (ED), which can be dosed on-demand or daily. Tadalafil has a long half-life, so it has a long-lasting effect. Men with ED also have a preference for a treatment that is time-independent Aim To evaluate the efficacy and safety of tadalafil 20 mg with a dose of one tablet every three days in the treatment of erectile dysfunction among diabetic patients. Material and methods A prospective study was carried out on 22 men with diabetes who were examined with symptoms of erectile dysfunction satisfying the selection criteria at Center for Andrology and Sexual Medicine - VietDuc University Hospital from June 2020 to June 2021. These patients were treated with tadalafil 20 mg once every three days. Results There were 22 patients included in the study, mean age was 52.1 years old. The baseline degree of erectile dysfunction was mainly mild to moderate (accounting for 73%). The average IIEF-5 score before and after treatment was 12.2 and 19.3, respectively. The improvement of IIEF-5 score was statistically significant (p <0.05). Headache was the most common side effect, accounting for 13.6%, followed by facial flushing, nasal congestion, myalgia and back pain with 9.1%, palpitations and digestive disorders with 4.5%. Conclusion tadalafil 20mg dosed one tablet every three days for the treatment of erectile dysfunction among diabetic patients has a statistically significant effect; hopefully, providing an additional option for the safe treatment of erectile dysfunction in diabetic patients. Disclosure Work supported by industry: no.