Background: Many patients develop excessive response for gonadotropin stimulation through controlled ovarian stimulation (COS) cycle over the years, there was an increase in incidence of ovarian hyperstimulation syndrome (OHSS) which represents an important medical problem for the clinicians. Objectives: to compare GnRHa and hCG as ovulation trigger in patients with PCOS after controlled ovarian stimulation by estimation of ovulation rate and rate of clinical pregnancy in studied group and detect efficacy in preventing or reducing incidence of OHSS. Patients & Methods: This prospective study was carried out in the unit of Cytogenetic and Endoscopy in department of Obstetrics and Gynecology in Zagazig university hospital during the period from September 2017 to January 2018 where 52 subfertile women with anovulatory PCOS. Results: showed that there is no significant difference in the overall ovulation rate. The average rate of ovulation was 38 (33.04%) and 30 (26.06 %) in GnRHa and hCG groups. The OHSS incidence was higher in hCG group than the GnRHa group. Conclusions: hCG was the gold standard for complete oocyte maturation, the new agent seems to be GnRHa with its potential advantages over hCG trigger in OHSS reduction.