Twenty five crossbred (1f4 Finnish + 3f4 Rahmany) male lambs weighed 19.2 kg on average and aged 4 months were used in a 182 day feeding trial. Animals were randomly divided into five equal groups (5 animals each )to study the effect of feeding chemically and biologically treated corn stover residues on animal performance, nutrients digestibility, carcass characteristics and feed efficiency. The experimental lambs were randomly assigned into five experimental rations as follows: C (control) : 2% of LBW CFM ( concentrate feed mixture) and. berseem hay ad lib ; ration T1: 2 % of LBW CFM and fungus (Iherfzanum F—416) plus yeast culture (S. cerevisiae) treated corn stover with 1% urea and 3% El-Mufeed ad ifb, ration ; T2: 2 % of LBW CFM and yeast culture (Scarevisiae) treated corn stover with 1% urea and 3% El-Mufeed ad lib ; ration T3: 2 % of LBW CFM and corn stover silage with 3% Ei-Mufeed ad fit: ; ration T4: Ration T3 plus 5gm fh id of dried baker's yeast culture (Scerevisiae), respectively. Results showed that digestibility coefficients of all nutrients except of DM were higher with T1(fungus plus yeast) than those in C,T2,T3 and T4 rations .While, ration of corn stover silage (T3) had the lowest values of DM.OM and CP digestibilities . Also, treated corn stover with fungus plus yeast or with yeast only led to significantly (9:10.05) increased CP digestibility than corn stover silage rations (T3 and T4, respectively). Nutritive values as TDN and GOP were the highest with both rationsT1,coculture (69.64 % and 11.10%) and control, C (69.16% and 11.67%) ,respectively than those of the other rations. The differences were significant (Ps0.05) with both TDN and DCP values. The ruminal parameters (pH and NH3—N) recorded the highest values with corn stover silage ( T3 ) ration compared with the other rations ; while, the highest (9:10.05) values of TVFA's were obtained with T1 (coculture) ration compared with the other rations. Average total DM intake (gfhfd) was significantly (Ps0.05) decreased with groups fed rations of T1,T2 ,T3 and T4 by 30 56. 27.71, 32.62 and 31.34 %, respectively compared with the control group. Similar trend was observed with feed intake (gihfd) as TDN and DCP between the tested groups and the control group. Average daily weight gain (gfh) was improved significantly (P<0.05) for group < /p> T1, coculture (135.17) compared with the other groups . Feed conversion (kg 1' kg gain) as DM and TDN was improved significantly (Ps0.05) with lambs fed T1 ration followed by T4 , T3 and then T2 ration, respectively than those fed the control ration .Whereas, kg DCP! kg gain showed the best value with lambs fed both rations of T4 and T3 ( silage rations) followed by T2 and then T1 ,respectively compared with the control. Dressing percentage %(as fasting body weight) was significantly (P<0.05)