This study was conducted to investigate the effects of different dietary levels of L-carnitine on body weight, feed intake, metabolizable energy (ME), semen characteristics and some blood biochemical's of Gimmizah cocks. Forty eight cocks of 60 weeks old were randomly chosen from a large flock with insignificant differences in body weight  and divided into 6 groups (8 birds in each ) according to L-carnitine supplementation level ( 0.0, 25, 50, 75, 100, and 125 mg L-carnitine/kg of diet). Birds were housed in individual wire cages during the whole experimental period from 60 to 68 weeks of age. The results indicated that body weight, body weight change and feed intake were not significantly affected by dietary L-carnitine supplementation. However, the efficiency of ME utilization was improved in response to dietary L-carnitine supplementation compared with the control.  Ejaculate volume, testes absolute and relative weights, sperm motility, livability, normality percentage, and sperm concentration, were significantly increased by increasing supplemental L-carnitine level. Also, blood plasma concentrations of total protein, albumin, albumin/ globulin ratio and glucose were significantly (P≤0.05) increased by feeding the L-carnitine-supplemented diets; however, globulin was not affected. Cholesterol and total lipids concentrations were significantly (P≤0.05) decreased by dietary L-carnitine supplementation. It could be concluded that the addition of L-carnitine in cock diets proved to be effective in improving the utilization of dietary ME and semen characteristics of aged Gimmizah cocks..