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 1 st group (T1) was fed the basal diet and served as a control group (without supplementation). The 2 nd group and 3 rd 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 folliclestimulating 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.