his experiment was conducted to study the effect of biological and chemical treatments of olive trees by-products on chemical composition, degradability, cell wall constituents, digestibility and nutritive value and its feeding effect on productive performance of growing sheep. Eighteen (½ Finnish Landrace × ½ Rahmani) lambs with average body weight 18.00±0.40 kg and 4 months old were used in this study for 120 days. Lambs were distributed into three similar groups (6 lambs each) and randomly assigned to three experimental rations. The three respective rations composed of concentrate feed mixture (CFM) + olive trees by-products, the control ration (R1) contained untreated olive tree by-products; (R2) treatedolive trees by-productswith EM1 and (R3)treated olive trees by-products with El-mofeed. The digestibility and nutritive values of experimental rations were determined using nine adult Ossimi rams. Rumen liquor and blood samples were collected at the end of collection period. The results showed that nutrient digestibility and feeding values (TDN and DCP) were higher (P<0.05) for rations containing treated olive trees by-products than control. The highest values of TDN and DCP were observed for R2. Digestibility of cell wall constituents (NDF, ADF, cellulose and hemicellulose) were improved by treatments. Concentrations of rumen parameters (NH₃-N and TVFA's) were significantly (P<0.05) increased by treatments. However, no significant (P>0.05) differences were found in blood constituents (total protein, albumin, globulin, GOT, GPT and urea) among the different experimental groups. Blood sereum constituents were generally normal in all experimental groups. Growth performance with respect to total body weight gain and average daily gain (ADG) were improved by biological and chemical treatments. The same trend was observed for feed conversion and economic efficiency and the best values were recoded with R2. It was concluded that inclusion of biologically treated olive trees by-products to rations of growing (½ Finnish Landrace × ½ Rahmani) lambs could improve their performance especially treatment of olive trees by-products.