This study was conducted to evaluate the effect of dietary supplemental of glycine (Gly) on modulating physiological and reproduction performance of Mandarah (M) local chickens. A total of 135 hens and 18 cocks, from 28 to 40 weeks of age were randomly assigned to 3 treatments, and each treatment (T) include 45 hens and 6 cocks divided in 3 replicates of 15 hens and 2 cocks each. The 1st group (T1) was fed the basal diet and served as a control group (without supplementation). The 2nd group and 3rd group were fed the basal diet supplemented with 0.1 and 0.2 %, Gly (1 and 2 gm/ kg diet), respectively.). The study showed that the cocks Gly treatments (0.1 and 0.2 %) were significantly (P<0.05) increased in the ejaculate volume, total sperm output, semen quality factor, total motile sperm, thyroxine (T4) and follicle-stimulating hormones (FSH) compared with control treatment. Chickens that received diet supplemented with 0.1 % Gly had significant higher sperm concentration, total antioxidant capacity (TAC), triiodothyronine (T3) than those of control T1. No significant differences among T2, T3 and control (T1) in sperm motility %, live sperm %, dead sperm %, abnormal sperm %, fertility, hatchability, catalase, glutathione enzyme and luteinizing hormone (LH). Conclusively, it could be recommended to supply layer diets with Gly for better physiologically performance during the laying period.