Purpose: to assess safety and efficacy of autologous mesenchymal bone marrow stem cell injection in penile cavernosal tissue for erectile dysfunction therapy in diabetic men. Methods: The subjects of this study were diabetic men suffering erectile dysfunction, non-responding to maximum dose of oral PDE5I. Mesenchymal bone marrow stem cells were aspirated and injected after preparation in both corpora cavernosa at 3, 9 o’clock position. Erectile function was assessed by the International Index of Erectile Function and penile Doppler study, before and after 6 months after injection. Results: 4 patients out of 10 achieve hard erection adequate for satisfactory coitus, and 2 patients achieved penile hardness with addition of pharmacological therapy with sildenafil 100mg. Peak systolic velocity increased significantly in 4 patients (2 arteriogenic and 2 mixed erectile dysfunction), from 12∼22 cm/s to 32∼69 cm/s. Variations in end-diastolic velocity increased substantially in 2 patients with venogenic insufficien- cy alone at follow-up from 4∼5 cm /s to -4∼-3 cm/s. Conclusions: Despite promising stem cell treatment efficacy for patients with erectile dysfunction, more clinical studies and researches are still warranted.