An in vitro study was conducted to examine the influence of alcohol-fermented feedstuff formulated with byproducts on the fermentation characteristics and NDF disappearance in the rumen. Dietary treatments were either a soybean curd-based alcohol-fermented feedstuff (AFS) or brewery grain-based alcohol-fermented feedstuff (AFB). The AFS and AFB are composed of 50% commercial beef cattle feed, 50% soybean curd dreg, 5% molasses and 0.5% yeast and 25% commercial beef cattle feed, 25% brewery grain, 25% soybean curd dreg, 25% corn grit, 5% molasses and 0.5% yeast, respectively. The change of ammonia, pH alcohol, volatile fatty acids, and NDF disappearance were measured at 0, 2, 4, 8 and 12 hr after in vitro incubation in the rumen. After 2 hr incubation, higher ammonia concentrations were resulted in AFS (12.47 mg/dl) and AFB (12.85 mg/dl) compared to control (11.84 mg/dl) (p<0.05). Ruminal pH of AFS and AFB were significantly higher than control during 1 to 6 hr fermentation, but the pH of AFS and AFB were decreased after 6 hr. At 12 hr fermentation, the alcohol concentration of AFS and AFB was significantly increased by 43.9% and 48.0%, respectively. The acetate concentration was rapidly decreased in control, while the concentration was slowly decreased in AFS and AFB with increasing the fermentation time. Lower concentrations propionate and butyrate were observed in AFS and AFB during every fermentation time (p<0.05). The NDF disappearance was significantly lower in AFS and AFB after 4 hr fermentation. These results suggest that alcohol fermented feedstuff can control the fermentation pattern in the rumen.