Twenty crossbred male lambs (Finn-Ossimi) were randomly assigned to four nutritional groups, to receive one of the following experimental rations for 83 days. Treatments were; R1: 75% CFM +25% BS; R2: 75% CFM + 23% BS + 2% (NAHCO3) /kg DM; R3: 75% CFM + 25% BS + Monensin 33mg/kg DM and R4: 75% CFM + 23% BS + 2% NAHCO3 /kg DM + Monensin33mg/kg DM. Experimental rations used, based on concentrate pelleted feed mixture (CFM, 13.13% CP) and berseem straw (BS) as the daily roughage source. The main objective of the study was to evaluate the effect of dietary sodium bicarbonate and monensin supplementation to growing male lambs rations on ruminal fermentation activity and lambs growth performance. Animals live body weight, daily weight gain, feed intake (g/h/d) and feed conversion ratio (kg intake/kg gain) were estimated. A metabolic trial was conducted to evaluate experimental rations digestibility, Nitrogen balance (NB) and ruminal fermentation measurements. Results obtained indicated that addition of dietary (NAHCO3) 2% (T2), resulted in an increase (P<0.05) in total dry matter intake (TDMI) , different digestion transactions, pH value, concentrations of TVFA's , lambs FC ratio and daily gain(g) compared with the control group. However, rumen NH3-N and N balance were not affected, while total feed costs /Total kg gain (LE) ware increased. On the other side, with the addition of   Monensin at 33mg/kg DM (T3), it resulted in an increase (P<0.05) in total feed costs /Total kg gain (LE) and an improvement in lambs FC ratio. On the contrarily, ruminal measurements and N balance were not affected. Dietary Monensin supplement led also to an improvement in lambs digestion coefficient and daily gain (g), but with lower (P<0.05) daily feed intake; while adding dietary (NAHCO3) 2% with Monensin 33 mg/kg DM (T4) led to increase (P<0.05) lambs pH value, lambs daily gain, different digestion coefficient and Total feed costs /kg gain. However, ruminal TVFA's, NH3-N, DMI/h/d and N balance were not affected. On the light of the present results, it could be concluded that, supporting growing male lambs ration with both of 2% sodium bicarbonate and/or monensin (33mg/kg DM) might lead to an improvement (P<0.05) in rations digestibility and nutritive value, lambs feed conversion ratio and maximize lambs net profit gain (LE).