Objective To investigate whether an insulin sensitizer has any effect on amenorrhea and clinical and biochemical hyperandrogenism in Chinese women with polycystic ovarian syndrome (PCOS). Design Randomized controlled double-blind trial. Setting A tertiary referral center, Hong Kong. Patient(s) Chinese women who fulfilled the Rotterdam criteria of PCOS (n = 70). Intervention(s) Rosiglitazone 4 mg daily for the first month followed by 4 mg twice daily for 11 months. Main Outcome Measure(s) Menstrual status as well as clinical and biochemical hyperandrogenism. Result(s) There is a significantly higher rate of regular menses among the treatment arm (16 [50.0%] of 32 vs 4 [11.8%] of 34) at 6 months and the improvement appeared to be sustained (10 [41.7%] of 24 vs 6 [20.0%] of 30) at 12 months. There was no change in the acne and hirsutism scores as well as serum T levels in both arms. Conclusion(s) We found a possible benefit in menstrual cyclicity but a lack of improvement in hyperandrogenism in our Chinese population. Clinical Trial Registration Number ChiCTR-TRC-09000670 (Chinese Clinical Trial Registry).