The objective of this study was to evaluate the effect of increasing levels of crude protein of crambe meal (Crambe abyssinca) (0, 25, 50, and 75%) on blood serum urea levels of lambs. Twenty-four Santa Inês crossbred male lambs, with an average weight and age of 18 kg of body weight, and 4 mo, respectively. The experiment was conducted in a completely randomized design with 4 treatment and 6 replicates each. Animals remained 7 d for adaptation, and 3 periods of 28 d for data collection. Lambs were kept in individual pens (1.5 m x 1.0 m), equipped with trough and drinker. Animals received diets with 19% crude protein (% DM), and 65.4% total digestible nutrients (% DM), based on average daily gain of 200 g head⁻¹ with forage: concentrate ratio of 50:50. Lambs were fed ad libitum, twice a day, always at 0700 and 1500 h, allowing leftovers of approximately 20%. Sampling of urea serum in the lambs were through blood samples taken by puncture of the jugular vein at 13th day of the second experimental period immediately at 0, 3, 6 and 9 h after the morning feeding. Data were subjected to ANOVA and regression, at 5% probability. The blood serum urea level did not differ (P > 0.05) among treatments and 25.96, 25.65, 24.23, and 21.70 g day⁻¹, respectively, for diets with 0, 25, 50, and 75% crude protein inclusion of crambe meal. This result demonstrates the appropriateness of the use of nitrogen compounds in the rumen due to the availability of degradable organic matter. Therefore the use of crambe meal on diet has satisfactory effect with regard in lamb blood serum urea.