Objectives: Studies evaluating the effects of mandibular advancement device (M.A.D) in Chinese are lacking. This is important as the craniofacial morphology between Chinese and Caucasians are different. The aim of this study was to evaluate the short term effectiveness and side effects of M.A.D on Chinese patients with obstructive sleep apnea (OSA). Methods: Fifteen (9 males and 6 females) patients of mean (SD) age 42(21) years, body mass index 25.7 (3.9) kg/m² and neck circumference 38.3(3.2) cm were diagnosed with OSA by overnight polysomnography. Baseline apnea/hypopnea index (AHI) was 38.2(17.2) events/hour. Minimum arterial oxygen saturation (SaO2) was 75.5(11.1) % and Epworth sleepiness score (ESS) was 8.9(4). Treatment success was defined as 50% reduction in AHI with AHI less than 20. Pretreatment and post-treatment variables were compared using Wilcoxon sign rank test and the statistical significance level was set at 5%. Assessment of snoring and side effects were evaluated with questionnaires. Results: Four patients dropped out of the study. Eleven patients (6 males, 5 females) wore the M.A.D (Intraoral Snoring Therapy, Scheu Dental, Germany) for an average of 5.4 months before a second polysomnogram was done with the appliance in situ. The body mass index and neck circumference of 23.4(1.8) kg/m² and 37.1(4.0) cm respectively did not differ between the two time points. AHI was significantly reduced to 10.9(14.7) events/h. Minimum Sa02 was significantly increased to 86(8.4)% . Treatment was successful in ten out of eleven patients (91%). ESS was significantly reduced to 4.8(3.4). Snoring was reduced in ten out of eleven (91%) patients. All patients experienced minor temporary side effects which included teeth soreness in 8(72%), a sense of altered bite in 7(64%), muscle soreness in 3(27%) and increased salivation in 2 (18%). Conclusion: M.A.D is an effective treatment and is well tolerated in Chinese patients with OSA.