Abstract: To investigate the effects of melatonin（MT） on chronic heat stress in laying hens, 60 Hyland’s brown-shelled laying hens were randomly divided into four groups: control group（Control）,heat stress group（HS）, heat stress melatonin low-dose group(HS+MT 1 mg·kg^-1), and heat stress melatonin high-dose group(HS+MT 5 mg·kg^-1). The results showed that the addition of MT to feed increased serum MT concentration, feed intake and egg production rate in heat-stressed laying hens.The serum levels of glutathione peroxidase（GSH-Px） and follicle-stimulating hormone（FSH） in heatstressed laying hens were significantly increased after MT treatment, and the serum levels of corticosterone（CORT）, heat-shock protein 70（HSP70）, malondialdehyde（MDA）, interleukin 6（IL-6）and interleukin 1β（IL-1β） levels were significantly decreased after MT treatment. The thickness of the granulosa cell layer and follicular membrane layer of the large yellow follicle（LYF） increased.Compared with the HS group, the expression levels of ovarian gonadotropin-releasing hormone（GnRH） and its receptor（GnRHR）, follicle-stimulating hormone receptor（FSHR）, glycoprotein hormone receptor（LHCGR）, and estrogen receptor 2（ESR2） were elevated in the HS+MT 1 mg·kg^-1 group, while the expression level of HSP70 was decreased. In conclusion, exogenous MT could effectively enhance the antioxidant and anti-inflammatory capacity, regulate immunity, protein metabolism and hormone levels, and improve production performance in heat-stressed laying hens.