In this study, the effects of different protein sources on microbial protein synthesis were examined. Four Kivircik X Morkaraman (G1), wether fed with maize silage based diets, fistulated with duodenal and ruminal canula and weighing 54.22 kg in average were used in 4x4 Latin Square experimental design. The research was completed in 4 periods each lasted 22 days. The diets were prepared in izocaloric and izonitrogenic on dry matter basis, Soybean Meal (SM), Vetch (V), Chickling Vetch (CV) and maize Gluten Meal (GM) were used in rations as protein source. The animals were housed in individual pen and adlibitum fed. Animals consumed fresh water freely as they needed. Dry Matter (DM), Crude Protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Organic Matter (OM), Ammonia Nitrogen (NTH3-N) in the duodenal samples and microbial purin, Volatile Fatty Acids (VFA), CP, NH3 levels in the ruminal samples were determined in present study. The amounts of Microbial Crude Protein (MCP), CP sourced from feedstuff (By-protein), ammonia nitrogen (NH3-N) and digestion rates of nutrients in the duodenal digesta were calculated using different equations. The indicator methods, CrO2 absorbed NDF and microbial purin were used to determine the digestion rates of nutrients and microbial protein in the duodenal digest. The differences among the group means were significant (p<0.05) for amounts of acetic butric and propionic acids but not significant for the time of the post feeding. The amounts of the acetic, butric and propionic acids groups were 45.04, 4.32, 9.35 mmol L-1 for SM; 82.96, 7.71, 17.81 mmol L-1 for V 64.17, 7.72, 14.48 mmol L-1 for CV and 65.72, 7.67, 20.56 mmol L-1 for GM. The differences among the groups were significant (p<0.05) for rumen NH3 concentration but not significant for pH value. The differences in NH3 concentration between 2nd and other post feeding times (h) and the differences in terms of the pH value between 0th and other post feeding times were significant (p<0.05). The NH3 concentrations and the pH values for the groups were 16.98, 14.27, 14.58, 14.18 mg 100 mL(-1) and 6.25, 6.24, 6.11, 6.09, respectively. The difference among the groups were significant (p<0.05) for the digestible CP but not significant for true digestibility of the DM, CP, NDF, ADF and OM. Digestibility rates fare nutrients were calculated as 55.71, 57.83, 57.83, 51.33, 62.58% for SM, 63.02, 60.43, 52.13, 40.93, 78.66% for GP, 77.37, 76.81, 69.54, 57.84, 78.66% for BB, 72.72, 64.87, 45.07, 33.70, 66.19% for GM, respectively. The differences among the groups in the duodenal digest was significant for by-pass-N (p<0.05) but not significant for NH3-N and MCP. The amounts of by-pass-N, MCP and NH3-N were as 8.81, 5.71, 5.06, 9.83 g; 32.41, 16.91, 21.96, 51.25 g; 105.79, 98.56, 115.53, 102.63 g, respectively.