The purpose of this study was to determine if inoculation at ensiling with a fibrolytic enzyme (xylanase plus cellulose; XC) or bacteria [Promote ASB (Lactobacillus buchneri and L. plantarum); PRO] would improve sorghum (Sorghum bicolor) silage nutritive value and fermentation characteristics. This completely randomized factorial experiment (cultivar × location × inoculant) evaluated 4 cultivars [PS 747 (PS), dairy master BMR, dairy silo 700, and MMR 381/73 (MMR)] planted in triplicate plots in College Station or Beeville, TX. Inoculant was added to 200 ml distilled water (control) and applied to 5 kg of chopped sorghum at a rate of 1.34 ml XC or 16.5 mg PRO prior to ensiling. Sorghum was harvested at 5 cm stubble height and herbage mass was not different (P < 0.01) among locations. The greatest yield (P < 0.01) was for PS and the least for MMR (16.47 and 10.18 ± 1.3 Mg ha^-1, respectively). All values are reported on a dry matter basis. Neutral detergent fiber concentration was least (P < 0.04) for silage treated with XC, and acid detergent fiber concentration was lower (P < 0.01) for silage treated with XC or PRO. Treated silage had greater (P < 0.04) crude protein (6.8 ± 0.1%) and water soluble carbohydrate (8.5 ± 0.7%) concentrations. Ammonia N was not affected (P < 0.31) by inoculant, and inoculation decreased (P < 0.01) pH. Lactic acid concentration was greatest (P < 0.01) for PRO, whereas, acetic acid concentration was greater (P < 0.02) for XC and control. Butyric acid concentration and mold count were not different (P < 0.40). Inoculant XC increased (P < 0.24) aerobic stability by 15 h longer than the control. Treating sorghum silage with these inoculants reduced the fiber fraction suggesting an increase in cell wall degradability and improved fermentation characteristics.