This study was conducted to assay the using of non- conventional energy sources on chemical composition, digestibility coefficients, cell wall constituents, nutritive value and productive performance of growing Rahmani lambs. Twelve Rahmani lambs with average body weight 22.60±0.20 kg and 4 months old were used in this study for 120 days. Lambs were distributed into two similar groups (6 lambs each) and randomly assigned to two experimental rations. The two respective rations composed of R₁ (control) contained 60% concentrate feed mixture (CFM)+40% rice straws(RS). While, R₂ consisted of 55% CFM + 40% RS + 5% corn steep liquor (CSL).The digestibility and nutritive values of experimental rations were determined using six adult Rahmani rams. Rumen liquor and blood samples were collected at the end of collection  period. The  results showed that nutrient digestibility and feeding values were higher (P<0.05) for rations R₂. The highest values of TDN and DCP were observed R₂. Digestibility of cell wall constituents (NDF, ADF, cellulose and hemicellulose) were improved by treatment. Blood constituents were generally normal in all experimental groups. Growth performance e.g. total body weight gain and average daily gain was improved in R₂. The same trend was observed for feed conversion and economic efficiency and the best values were recoded with R₂. It could be concluded that addition of CSL to ration of growing Rahmani lambs could improve their productive performance and economic feed efficiency.