An investigation was undertaken to study the effects of feeding mango seed kernel (MSK) as partially substituting of yellow corn on productive performance and physiological parameters of Gimmizah cockerels. A total number of 100 Gimmizah cockerels aged 28 days were distributed into four groups. Each group was represented by five replicates (5 cockerels per rep.) from 4 -16 wk of age. The first group (control) fed the basal diet. The second, third and fourth groups were fed the basal diet with the substitution of yellow corn with MSK with 10, 15 and 20%, respectively. Body weight and body weight gain were increased when used 10% level of MSK. Feed consumption was significantly decreased and feed conversion was significantly improved overall period for 10% MSK.  Carcass characteristics had not affected. While, blood constituents (Hb, PCV%, RBCS, and WBCS counts) were significantly improved. Lymphocyte (L) count for birds fed 10 and 15% MSK was significantly increased and heterophils (H) count and H/L ratio was significantly decreased. The immunological status was significantly improved due to an increase in globulin, IgG and IgM for cockerels fed diets containing the MSK levels (10%,15%). Plasma cholesterol, CK and MDA was significantly decreased by increasing MSK levels. Serum alkaline phosphatase (ALP) activity was significantly reduced when a cockerel fed diet containing 10 and 15% MSK. Bacterial count in the intestine and in fresh breast and thigh meat were decreasing by increasing MSK levels. All MSK levels used were shown better economic efficiency than the control group. The relative economic efficiency of 10% MSK replacement of corn increased with 48% than the control group. It could be concluded that MSK can be used up to 10% without any adverse effect on performance and improve blood parameters and the economic efficiency of Gimmizah cockerels during the growing period.