The objective of this study was to evaluate the effect of virginiamycin (VM) combined with crude glycerin (CG) on pH value, N-NH₃ (mg/100 mL) and VFA (mM). Rumen fistulated bulls (BW = 600 ± 34 kg) were used in a replicated 4 × 4 Latin square (21-d periods) with 2 × 2 factorial arrangement of treatments: diets without virginiamycin (VM-) or with 25 mg/kg of VM in DM (VM+) combined with diets without crude glycerin (CG-) or with 100 g/kg of CG (80% glycerol) in DM (CG+). The sugar cane bagasse was used as the exclusive roughage in the proportion of 20% in DM of diet and crude glycerin replace corn in the diet formulation. Diets were offered on an ad libitum basis at 0700 and 1600 h. Ruminal samples were taken immediately before feeding and at 3, 6, 12, 18 h post feeding on d20 and d21 of the sampling week. Data were analyzed in a replicated 4 × 4 Latin square with a 2 × 2 factorial using the MIXED procedure of SAS (SAS Inst., Inc., Cary, NC). Statistical model included the fixed effect of virginiamycin (1 degree of freedom, DF), crude glycerin (1DF) and all interactions. Random effects were period (3DF), bulls (3DF), and residual error. There were no CG × VM interactions for any variable measured (P > 0.05). Diets with CG or VM had similar values of pH (mean = 6.15; P > 0.05). CG+ had lower N-NH₃ concentration compared with CG- diets, independent of VM inclusion (24.26 vs. 28.69 mg/100mL; P > 0.05). Data showed that CG or VM did not affect the concentration of total VFA (116.92 mM; P > 0.05). The molar proportion of acetate was lower in CG+ compared with CG- diets (53.58 vs. 62.70% of total VFA; P < 0.01) and it was greater in VM- compared with VM+ diets (59.60 vs. 56.68%; P < 0.01). The molar proportion of propionate was greater in CG+ than CG- diets, independent of VM inclusion (24.47 vs. 18.54%; P = 0.0091). The molar proportion of isobutyrate and isovalerate were not affected by CG or VM (P > 0.05). Acetate:propionate ratio was lower in CG+ compared with CG- diets (3.57 vs. 2.36; P > 0.05). Valerate and butyrate proportion was greater in CG+ than CG- (P < 0.05). CG can replace corn at 100 g/kg of DM and VM in Nellore finishing diets without impairing fermentation.