Aim: To compared the efficacy of Metformin and NAC on clinical, metabolic, hormonal, sonographic and fertility aspects among PCOS patients. Material and methods: A prospective, comparative study was conducted in the Department of Obstetrics & Gynaecology, NSMCH, Bihta, Patna, Bihar, India, for 1 year. 120 women with PCOS (diagnosed by Rotterdam criteria) of age group 18–37 year were included in this study. Serum TSH, serum prolactin, serum follicle-stimulating hormone, luteinizing hormone (mIU/L), LH/FSH ratio, serum fasting insulin, serum fasting glucose level, serum fasting glucose/insulin ratio and serum total testosterone were measured by enzyme immune assay(EIA). Ultrasonography examination (TAS and TVS) was done preferably on day 2 or 3 of menstruation. Subjects were randomly assigned into two treatment groups. Group M received metformin 500 mg three times a day. Group N received N acetyl cysteine, 600 mg three times aday. Results: Out of 120 cases, 20 were lost to follow-up. In remaining 100 cases, 50 were in Group M, 50 were in Group N. The cases in Group M received tab metformin 500 mg three times a day, and Group N received tab N acetyl cysteine 600 mg three times a day. After 24 weeks of treatment with either metformin or NAC clinical characteristic, metabolic parameter and hormonal profile were re-evaluated. There was no significant reduction of weight in both the group after treatment, while a significant reduction of BMI, WC and WHR was found in Group N receiving NAC. Fasting glucose and fasting insulin were reduced in both groups significantly. There was a significant improvement of fasting glucose/insulin ratio in both groups. Total testosterone was significantly reduced in Group N. Conclusion: we concluded that the better improvement of metabolic and hormonal profile was observed in N acetyl cysteine group. Because of its less side effect comparing to metformin, NAC can be used as a substitute for insulin-sensitizing agent in treatment of PCOS.