Introduction: Poor ovarian response to exogenous gonadotrophins occurres in 9-26% of ART cycles. Ovarian reserve decreases by ovarian aging which is an important factor in decreasing ovarian response to gonadotrophins but there are other probable methods which are reported as affecting factors on ovarian response to gonadotrophins such as high dose of gonadotrophins, adjuvant therapy with growth hormone and glucocorticoids. In this study, we aimed to evaluate the role of Dexamethasone, as an effective factor on ovarian response, in infertile women aged over 35 years who referred to Royan institute. Material and methods: In this clinical trial, 72 infertile women, aged over 35 years, who referred to Royan institute to undergo IVF/ICSI program, were selected. Patient were divided into two groups in each group, 36 patients were studied. Laboratory tests including serum FSH, LH, Total Testosterone, Estradiol, Prolactin and thyroid function tests were performed on third day of menstrual cycle. Standard long protocol began on 21st day of menstrual cycle. Simultaneously, in triple blind method, each woman received either 2 tablets containing Dexamethasone or placebo. After 2 weeks, ovarian stimulation was started using 3 HMG ampoules from 2nd day of menstrual cycles and its dose was increased according to ovarian response. If the size of at least three follicles was more than 18 mm, HCG (10000 IU) was administrated after Estradiol measurement. After 36-38 hours of HCG administration, oocyte was retrieved by transvaginal sonography guidance. Embryo transfer was done after 48 hours. SPSS version 11.5 was used for data entry and results were analyzed by Paired t test and Chi-square. P v