A total of 300 females from each of Sinai and Mamourah local laying hens (150 each) were used to study the relationship between body weight, thyroid hormones and Leptin hormone and their effects on productive, physiological and immunological performance. Birds of each strain were classified according to their body weight into three groups (high, medium and low). Each group of each strain containing 50 females was equally subdivided into 5 replicates for the experimental period (20- 40 weeks of age). Body weight and feed consumption were recorded every four weeks, egg production (egg number, egg weight and calculated egg mass) were detected daily. Also, egg quality traits were taken at the end of the experimental period. At the end of the experimental period, five birds / group were chosen randomly slaughtered and blood serum samples were collected to determine calcium , phosphorus , total protein , albumin , globulin , cholesterol, LDL, HDL, total lipids , glucose, Leptin , T3, T4 , LH and FSH hormones .Results indicated that : -Mamourah hens had significantly higher body weights and consumed the largest amount of feed compared with Sinai ones. - Age at sexual maturity was delayed for hens of low body weights compared with those for high and medium body weights for both chicken strains. - Medium body weight groups for both strains represented the highest numerical increase for egg weight and egg mass followed by the high weights and lastly the smallest ones. - Eggs produced from low body weight hens recorded significant increase in shell thickness and Haugh units compared with eggs for high body weight hens.Mamourah hens had a higher absolute and relative albumen weight than Sinai hens. - Levels of serum Leptin and thyroid hormones T3 and T4, calcium, phosphorus, total protein, albumin, globulin, LH and FSH hormones were increased in low and medium groups compared with high groups. - Levels of serum glucose, cholesterol, LDL, HDL and total lipids were decreased in low and medium groups compared with high groups. - The immune response against Newcastle and Avian Influenza diseases and spleen andthymus relative weights were increased in low and medium groups compared with high groups. - There were positive correlations between body weight, egg weight and egg mass, but it was negative between body weight and egg number. - Positive correlations between body weight, T3, T4 hormones, phosphorus and cholesterol were found. - There were negative correlations between body weight and Leptin, LH, FSH hormones and calcium. - Negative correlations between high levels of Leptinhormone and T3, T4 hormones and cholesterol were found. - There were positive correlations between high levels of Leptin hormone and increasing levels of LH, FSH hormones, calcium and phosphorus. It can be concluded that live body weight had an important role in regulating the release of some hormones which exert their effects on the productive performance of laying hens.