The objective of this study was to evaluate the effect of increasing levels (0, 25, 50, 75%) of crude protein substitution of the concentrate by crude protein of crambe meal on microbial protein synthesis and the flow of microbial nitrogen compounds in sheep. Four rumen fistulated sheep (18 months and initial average body weight of 50 kg) were distributed in a 4 x 4 Latin square design. Diets were balanced to meet the requirements for minimum gains, containing approximately 14% crude protein and 70% total digestible nutrients. The roughage to concentrate ratio was 50:50. The total urine collection was performed to determine the excretion of purine derivatives and to evaluate microbial nitrogen production and microbial protein synthesis efficiency. The results were submitted to analysis of variance and regression at 5% of significance. Even though a linear negative effect (P < 0.05) was observed for intake of total digestible nutrients, we have found a linear positive (P < 0.05) effect of crambe meal on microbial nitrogen compounds flow to the small intestine, relative intestinal nitrogen microbial flow, and efficiency of microbial protein synthesis. Thus, crambe meal can be used up to 75% of the crude protein of concentrate in diets for sheep since it improved the overall microbial efficiency.