Objective: To evaluate the effects of hyperbaric oxygen therapy (HBOT) on erectile functions and serum testosterone levels in patients with erectile dysfunction (ED).Methods: The patients treated by HBOT for several diseases between July 2017-May 2018 and had erectile dysfunction were included in the study. All patients filled the International Index of Erectile Function (IIEF) questionnaire form; serum total testosterone (TT) and free testosterone (FT) levels were examined before the first day and after the last day of HBOT. The effects of demographic characteristics of patients on erectile functions were evaluated. Patients were categorized according to the risk factors. The IIEF scores, TT and FT levels of patients in first day and after last day of HBOT were compared.Results: Totally 43 patients were included in the study. The mean post-HBOT IIEF-EF score was significantly higher than the mean pre-HBOT IIEF-EF score of patients (25.4 ± 5.3 vs 20.6 ± 5.1; p < .001). There was no statistical difference between the pre-HBOT and post-HBOT serum TT and FT levels of patients (4.0 ± 2.3 ng/ml vs 4.1 ± 2.0 ng/ml, p = .797; 8.6 ± 3.8 pg/ml vs 8.9 ± 3.5 pg/ml, p = .658).Conclusions: HBOT improved the erectile functions in ED patients however we cannot detect any effect on testosterone levels in our study.