GnRH agonist (GnRHa) has been reported to have direct effects and functional roles in the endometrium and embryos. Several meta-analyses have shown that GnRHa administration in the luteal phase improved the live birth rate or pregnancy rate in both fresh and frozen embryo transfer (FET) cycles. The aim of this study was to investigate whether luteal GnRHa administration could also improve in vitro fertilization (IVF) outcomes in patients undergoing hormone replacement therapy (HRT) cycles with GnRHa suppression. The retrospective cohort study included a total of 350 patients undergoing GnRHa-HRT FET cycles. The study group included 179 patients receiving an additional single dose of GnRHa in the luteal phase following embryo transfer. A total of 171 patients in the control group did not receive luteal GnRHa. The baseline and cycle characteristics and reproductive outcomes were compared between the two groups. Baseline and cycle characteristics were similar between the two groups, except lower AMH levels were found in the luteal GnRHa group than in the control group. The luteal GnRHa group had a significantly higher ongoing pregnancy rate and live birth rate than the control group. The multivariate analysis revealed that luteal GnRHa administration was positively associated with ongoing pregnancy (OR 2.04, 95% CI 1.20-3.47, P = 0.008) and live birth (OR 2.03, 95% CI 1.20-3.45, P = 0.009). When the subgroup of patients with recurrent implantation failure was analyzed, the multivariate analysis also showed that luteal GnRHa administration had beneficial effects on ongoing pregnancy (OR 4.55, 95% CI 1.69-12.30, P = 0.003) and live birth (OR 4.30, 95% CI 1.59-11.65, P = 0.004). Our data suggest that the addition of one luteal dose of GnRHa may improve the live birth rate in patients undergoing the GnRHa-HRT protocol.