To evaluate the effect of the oral-appliance combined with tadalafil in the treatment of erectile dysfunction (ED) induced by severe obstructive sleep apnea-hypopnea syndrome (OSAHS). We equally randomized 90 patients with severe OSAHS-induced ED to groups A, B, and C to be treated with the oral-appliance, tadalafil (10 mg daily qd), and oral-appliance plus tadalafil, respectively, all for 3 months. Then we compared the therapeutic effects among the three groups of patients using the IIEF-5 questionnaire, Sexual Encounter Profile (SEP) diaries, and the intercourse satisfaction rate of the patients' partners. Totally 87 of the patients accomplished the treatment, 29 in group A, 30 in B, and 28 in C. After treatment, group C, as compared with A and B, showed significant increases in the IIEF-5 score (4.18±1.19 vs 2.66±1.63 and 2.77±1.74, P=0.009 and P=0.026), the success rate of penile intromission (SEP2) (85.7% vs 58.6% and 53.3%, P=0.023 and P=0.008), and the success rate of intercourse (SEP3) (64.3%% vs 37.9% and 33.3%, P=0.047 and P=0.018). The overall satisfaction of the female partners was remarkably higher in groups A and C than in B (P=0.027 and P=0.007). Oral-appliance combined with tadalafil can improve erectile function in patients with severe OSAHS-induced ED, with a better efficacy than either of them used alone.