Six males Barki sheep with an average body weight of 45 kg were used in this study for feed evaluation and three female Barki sheep fitted with a permanent rumen fistulae were used to study the rumen activity.  The animals were fed four mixed diets supplemented with soybean meal (SBM),linseed meal (LSM),undecorticated cotton seed cake (UDCSC),  and urea as protein and NPN sources .Meat and bone meal (MBM) was added to all diets. Ratio of roughage to concentrate was 1:1.Data could be summarized as follow: 1-The highest dry matter intake ranged between 1005.98±76.34for urea diet and 1392.03±10.89 (g/day) for SBM diet with a significant difference (p < 0.05). 2- The total digestible nutrients (TDN% ) ranged between 61.56±0.95 for urea diet and 63.61±0.21 for SBM diet without any significant difference, while the digestible crude protein (DCP%) ranged between 9.54±0.13 for urea diet and 11.09±0.14 for SBM diet wiht a significant difference (p < 0.05). 3-Nitrogen balance ( N.B g/day) ranged between 1.88±0.30 for urea diet and 4.64±0.03 for SBM wiht a significant difference (p < 0.05). 4-Ammonia –N concentration (mg-N/100ml R.L.) ranged between 9.56±0.64 for urea diet 6.85±0.64 for UDCSC diet with significant difference .The rates of ammonia production( mg-N/100ml R.L./hr) ranged between 1.66±0.08 for UDCSC and 2.29±0.15 for LSM diet wit a significant difference (p < 0.05). 5-Volatile fatty acids (VFA's) concentration(m.eq/100ml R.L.) ranged between 7.19±0.26 and 8.63±0.37 for urea and LSM diets respectively with a significant difference (p < 0.05)Th rates of VFA's production (m.eq/100 ml R.L./hr) ranged between 1.95±0.11 and 2.40±0.06 for urea and LSM diets respectively with a significant difference (p < 0.05). 6- Rumen volume (L) showed the lowest value with the urea diet while the highest value was recorded with the LSM diet 3.21±0.19 and 4.60±0.10 (L) respectively with a significant difference (p < 0.05). 7- The microbial protein synthesis recorded the lowest value with the urea diet 33.26 and the highest value with the LSM diet 62.45 (g/day).