The aim of this study was to investigate the effect of partial substitution of concentrate feed mixture in the rations of growing lambs by ureated fodder corn silage (FCS) at different levels. A feeding trial for 135 days was carried out on twenty eight ½ Osimi x ½ Chios crossbred lambs of 6 months old and weighing 23.20 + 1.56 Kg LBW. Animals were divided into 4 groups (7 lambs each). The experimental groups allotted randomly into four rations control (R1): 3% CFM and 1% bean straw of LBW, while R2, R3 and R4 included 1, 1.5 and 2% CFM, respectively, while ureated fodder corn silage (FCS) ad-libitum. Feed intake, digestibility coefficients, nutritive values, nitrogen utilization, daily gain, feed conversion and economical efficiency were determined. Results indicated that the apparent digestibility coefficients of all nutrients and feeding value of rations containing silage (P<0.01) increased with increasing fodder corn silage except OMD,  compared to the control ration. Daily DMI expressed as Kg/h/d or DM/kg W^0.75   was significantly (P<0.05) higher in lambs fed rations containing different levels of FCS compared to those given the control ration. Lambs received silage recorded higher (P<0.01) average daily gain (ADG) than those received the control ration, the realized ADG were 174.44, 180.30 and 187.40 g/day for R2, R3 and R4, respectively, while lambs of the control recorded 156.5 g/day. Ruminal pH values, NH₃-N and total VFA'S concentrations showed that, using silage in rations of sheep had no significant effect, after 3 or 6 hrs post feeding. No significant differences were found among the experimental treatments in serum total protein, albumin, globulin, creatinine and urea-N. Feed conversion of lambs fed R2, R3 and R4 was markedly better than of the control group. Economical efficiency was better with the 1% CFM + silage ration (R4) than the other rations. Dressing percentage (on empty body weight) of groups fed silage containing rations was in favor of control. It could be concluded that, feeding ureated fodder corn silage (Darawa silage) ad-libitum with low level of concentrate feed mixture (1% of LBW of growing lambs diets), resulted in superior nutrition status and better daily gain, feed conversion and economical efficiency, as compared with other groups could be recommended.