Glycerin has the potential to partially replace starch-based ingredients in the diet, such as corn, because glycerol is converted to propionate in the rumen and acts as a precursor for hepatic glucose synthesis. The objective of this study was to evaluate the effects of crude glycerin (Gly) combined with protein sources on balance of nitrogen compounds of Nellore bulls fed tropical pasture during the rainy season. Five Nellore bulls (448.2 ± 14 kg; 25 ± 3 mo) were evaluated in a 5 × 5 Latin square design with 5 treatments and 5 periods. The animals were allocated into 5 paddocks of 0.25 ha, consisting of Brachiaria brizantha ‘Marandu’ in the rainy season. Crude glycerin (83.9% of glycerol) was used in all supplements to replace (15% of DM) corn. The supplements were: T1 - Gly with urea, T2 - Gly with soybean meal, T3 - Gly with cottonseed meal, and T4 - Gly with gluten, and the control supplement received mineral mixture ad libitum. Animals were individually supplemented at the rate of 300 g·100 kg⁻¹ of BW, daily, at 1000 h. The experimental period was the 17 d, divided in adaptation (14 d) and 3 d for collections the feces in different times. Urine samples were collected 4 h after the supplementation to determine the concentration of nitrogen, on the last day of period. Data were analyzed using the PROC MIXED of the SAS with α = 0.05 and F-test. Nitrogen intake (g·d⁻¹) was greater (P < 0.01) for Gly-urea compared with control and protein sources. There were differences in total grams of N excreted across treatments (P < 0.01). The increase in urinary and fecal N output by animals fed gly-urea contributed to greater total N output compared with other supplements. Nitrogen retained (g·d⁻¹ or % of N intake) was not affected by protein sources, but there were greater than control supplement (P < 0.01). Independently of protein source utilized, there was an increase of 59.5% (P < 0.01) in the N utilization (N retained, g·d⁻¹) for animals supplemented when compared with control group. Crude glycerin associated with protein sources can be efficient for improve the N utilization.