This study was conducted to evaluate the effect of different doses of GnRH on stress response in female koi carp (Cyprinus carpio). For this purpose, forty sexually mature female koi carp with an average weight of 102.05 ± 9.03 g were divided to four groups and fish received with a single intraperitoneal 0.9% NaCl with 20 mg kg^-1 metoclopramide (C); 10 μg kg body weight^-1 (BW) GnRH with 20 mg kg^-1 metoclopramide (Gn10); 20 μg kg BW^-1 GnRH with 20 mg kg^-1 metoclopramide  (Gn20); 50 μg kg BW^-1 GnRH with 20 mg kg^-1 metoclopramide (Gn50). Blood samples were collected before and after ovulation (approximately 24 h post-injection). The concentrations of plasma cortisol, lactate, and glucose were measured. Broodstocks who received GnRH spawned, while broodstocks of the group C did not spawn. The Gn10, Gn20, and Gn50 treatments led to significantly higher cortisol, lactate, and glucose concentration after ovulation compared to before injection (p< 0.05). The present results showed that females are highly sensitive to manipulation during reproduction and higher levels of the hormone cause more stress broodstocks, so they must be held with minimal disorders, especially during spawning period.