The cottonseed cake is a co-product obtained after extraction of oil cottonseed, and because of their bromatological characteristics has potential use in ruminant feed, can increase the economy efficiency of animal production systems. The objective of this study was to evaluate diets with cottonseed cake in substitution of soybean meal through nitrogen balance, microbial protein synthesis and the ingestive behavior of lambs. Forty crossbred Santa Inês × Dorper non-castrated rams with average initial weight of 20.9 ± 2.5 kg were distributed into a completely randomized design with four treatments and ten replicates, and fed diets containing cottonseed cake in substitution of 0, 33, 66 and 100% of soybean meal. The diets were composed of corn, soybean meal, cottonseed meal and hay, with forage:concentrate reason of 50:50, isonitrogenous, with 14% crude protein. The animals were confined individually in pens with slatted floor, the evaluations of ingestive behavior, which included observations of the feeding, rumination and idle times were performed in a period of 24 hours, in 5-minute intervals. At 97 days of experiment, a spot urine sample was collected from all animals to quantify the concentrations of nitrogen, creatinine, allantoin, uric acid, xanthine and hypoxanthine in the urine. The data were subjected to variance analysis and regression, adopting ?= 0.05. There was no significant difference between treatments for nitrogen balance, the synthesis of nitrogen compounds, and microbial efficiency. In addition, there was no effect of replacing soybean meal by cottonseed meal on feeding behavior of animals. Cottonseed cake can replace soybean meal up to 100% in diets for lambs.