Aims : To Evalavate the effect of N-Acetyl cysteine (NAC) A insulin sensitizer for failed ovualation with three or more cycles with clomiphene citrate (150 mg.) for ovualation induction. Design : Prospective Study Setting : Obstetrics and gynecology department of Sri ramchandra medical college and R.I. Patient (s) : One hundred patient who have failed to ovulate after ovulatia induction with clomiphene citrate 150 Mg. Aged 18-39 Yrs. undergoing therapy for infertility were included. Inter Vention(s) : 50 patients in the study group were given N-acetyl cysteine 1.2 gm/ day orally for 1 month, followed by ovulation induction with clomiphene citrate 150 Mg.