The objective of this Study was to evaluate the effects of different energy (barley and dry sugar beet pulp (DSBP)) and protein sources (soybean meal (SBM), SBM-treated with formaldehyde (FTSBM), cotton-seed meal (CSM)) on nutrient digestibility and nitrogen retention in sheep. In this study, 4 rumen fistulated Morkaraman rains were used. Digestibilities of dry matter, organic matter, crude protein, crude cellulose, ether extract, and N- free extract were similar (P>0.05) among animals fed different diets. Digestibitrties. as percentage were 79.49, 79.03,81,20, and 77,91 for DM; 80.38, 80.24, 83.37, and 80.49 for OM; 72.40, 70.52, 76.80, and 74.56 for CP; 67.00, 70.17, 73.87, and 65.03 for crude cellulose; 89.12,65.85,92.22, and 84.71 lor crude oil; 84.26. 86.03,87,29, and 85 59 for N-free extract for animals led bar-ley+FTSBM. DSBP+FTSBM, DS8P+SBM+CSM mixtures and commercial diet, respectively .The re was no significant differences on N-balance among animals fed different diets. N-retentions were 10.14, 7.22, 7,14, and 8.51 g for animals fed barley*FTSBM, DSBP+FTSBM, DSBP+SBM+CSM mixtures and commercial diet, respectively. Percentages of N retained in body and N digested were 60.36, 42,90, 42,84, and 51.05; 82,31, 80.93, 5658, and 68.46 for bartey+FTSBM, DSBP+FTSBM, DSBP+SBM+CSM mixtures, and commercial diet, respectively. It was suggested from these experiments Ihal; a) energy and protein sources didn't effect nutrient digestibility and nitrogen retention; b) formaldehyde treatment of protein source should be further studied; c) this results should be supported with fattening experiment to interpret the results safely.