Background: Aim of study is to evaluate effect of metformin on controlled ovarian stimulation and outcome of IVF. Method: Randomized controlled study was carried out, total of 50 women undergoing IVF, were divided to two groups: group A: control group (n= 24), and group B: metformin group (n= 26), who received metformin 500 mg t.d.s starting the cycle before ovarian stimulation till the day of serum β- hCG. Both groups were subjected to controlled ovarian hyperstimulation according to long protocol; fertilization in all cases was done by ICSI. Results: Both groups were similar regarding demographic data and management. Metformin group showed no evidence of statistically significant difference regarding duration of stimulation (P=0.72), units of gonadotropins needed for stimulation (P=0.86), total number of follicles obtained (P= 0.59), fertilization rate (P= 0.40), β-hCG (P=0.60), OHSS incidence (P=0.36). Conclusion: metformin as co‐therapy with controlled ovarian hyperstimulation does not seem to facilitate IVF stimulation or to improve the outcome of IVF treatment.