The objective of this study was to evaluate the effects of treatment with urea (0 and 6%) and fibrolytic enzymes (0, 2, 4 and 6%; 75% cellulase and 25% hemicellulase) on chemical composition, IVDMD, dry matter in vitro degradability (IVDEG), and gas production of cotton gin trash. A completely randomized design in a 2 × 4 factorial design was used, with 4 replications. Two kilograms of residue were treated by 60 d with urea dissolved in water, applied to raise the moisture to 25%. The enzymes were sprayed, acting for 24 h. There was significant interaction between urea and fibrolytic enzymes for DM, EE, CP, and ADF (P < 0.05). Urea treatment increased CP in 157% (P < 0.05). Enzymatic hydrolysis affected quadratically CP in the untreated residue, but positively linear when it was ammoniated. Urea and enzymes were an effective way in reducing cell wall constituents (P < 0.05). The IVDMD was greater with ammoniation and when the enzymes doses were increased (P < 0.05). There was no significant interaction between urea and fibrolytic enzymes on IVDEG (P < 0.05). Although the values of the fraction a decreased from 19.1% to 13.6%, ammoniation increased b and c fractions from 34.2% to 40.4%, and from 0.038 to 0.045, respectively (P < 0.05). Using 5% of passage rate, the addition of urea reduced the effective degradability from 33.9% to 32.6%. No effect of urea was observed for potential degradability (P > 0.05). Fibrolytic enzymes did not affect the soluble fraction (P > 0.05); however, they increased linearly all other IVDEG parameters. Urea did not affect the rate of digestion of K_d1 and K_d2 (P > 0.05), while the enzymes just decreased linearly K_d2. The Vf₁ and Vf₂ were greater with ammoniation (P < 0.05), increasing from 16.2 to 51.2 and 51.2 to 62.4 mL/g, respectively, and they were increased linearly with the enzymes doses. The lag time was affected by the interaction between urea and enzymes (P < 0.05), being different in the ammoniated material without or with 2% of enzymes. Urea and fibrolytic enzymes associated treatment enhanced nutritional value of cotton gin trash.