The aim of our study was to determine the effect of the dietary energy levels on the live body weight, testis volume and blood testosterone concentration in Ouled Djellal ram lambs throughout growth. The study lasted six months from post-weaning until the pubertal period at the Technical Institute Farms (I.T.E.L.V) Lamtar of Sidi-bel-Abbes (Western Algeria). After weaning, Twenty single-born Ouled Djellal ram lambs from 90 to 240 days old were weighed and allotted into two equal groups of Low energy (n = 10) or High energy (n = 10) nutrition plane. Each group received; in addition to a basal diet (good quality pasture) 200 g and 400 g of concentrate feed mixture containing barley (60%), corn (5%), wheat bran (37.5 %) and vitamin-mineral compound (2.5 %) by head-1day-1 respectively. Hay and water were provided ad libitum. Monthly measurements of live body weight, testicular volume and blood testosterone concentration of lambs were recorded. The results showed that the High energy group of lambs recorded a significantly higher live body weight compared to the lambs of low energy group (p <0.001). Whereas, the testicular growth indicated a gradual and linear increase for both groups (low energy and high energy) with significant differences (p <0.001). However, all measurements of the testis, live body weight, serum testosterone levels and age were positively correlated with one another of both low and high groups throughout the experiment. In conclusion, High-level energy supplementation can improve to enhanced development in Ouled Djellal ram lambs this may be due to its beneficial effect on the productive and reproductive performance of growing male lambs. Furthermore, using younger lambs may reduce production costs, accelerate the benefits of genetic selection, and allow earlier progeny and libido testing.