To investigate the effects of Yucca schidigera extract on fermentation characteristics in vitro, 5 treatments consisted of supplemental Y. schidigera extract at 0, 0.5, 2.5, 12.5 and 62.5 mg, which were assigned randomly to 6 of 30 incubation bottles together with 0.5 g TMR (therefore, the adding levels of Y. schidigera were 0, 1, 5, 25, 125 g/kg TMR), 50 mL basal media and 25 mL rumen fluid obtained from rumen-cannulated lactation Holstein dairy cows. Cumulative gas production was continuously measured in an automated trace gas recording system (AGRS-III, Beijing) lasted for 30 h at a 39°C incubator. All fermentation vessels were cultured in shaking incubator at 39°C for 30 h. All the data were analyzed by SAS9.2. Results showed that pH and microbial crude protein (MCP) were not affected by the treatments, while the average pH in the treatments were 6.6 ± 0.05, 6.6 ± 0.05, 6.6 ± 0.06, 6.6 ± 0.03 and 6.6 ± 0.04, the average MCP were 1.58 ± 0.025, 1.61 ± 0.034, 1.58 ± 0.049, 1.61 ± 0.018 and 1.67 ± 0.055 mg/mL, while the total gas production, in vitro dry matter degradability (IVDMD), neutral detergent fiber degradation rate (DNDF) and acid detergent fiber degradation rate (DADF) were improved (P = 0.028, P = 0.042) at the level of 25 and 125 g/kg TMR. The averages of the total gas production were 121.85 ± 0.034, 119.68 ± 0.037, 120.22 ± 0.037, 135.29 ± 0.041 and 130.35 ± 0.042 mL/g, respectively. The average percent of IVDMD were 60.48 ± 0.888, 62.45 ± 1.045, 62.22 ± 0.686, 64.55 ± 0.796 and 64.55 ± 0.765, while the DNDF were 43.24 ± 0.004, 43.28 ± 0.003, 43.69 ± 0.001, 44.72 ± 0.004 and 44.32 ± 0.003, and the DADF were 31.66 ± 0.003, 31.87 ± 0.007, 32.10 ± 0.001, 32.95 ± 0.001 and 33.01 ± 0.003, respectively. With the increasing levels of Y. schidigera extract, the concentration of NH₃-N was decreased (P = 0.042), while the acetate, propionate and total volatile fatty acids (TVFA) were increased (P = 0.030, P = 0.009, P = 0.048) after 30 h incubation. The mean values of NH₃-N were 39.60 ± 0.839, 36.18 ± 1.063, 35.07 ± 1.576, 34.28 ± 1.698 and 34.12 ± 1.073 mg/mL, while the TVFA were 65.72 ± 1.388, 67.04 ± 1.473, 73.52 ± 1.58,4 67.82 ± 1.824 and 72.57 ± 1.080 mmol/L, respectively. The results indicated that Y. schidigera extract was beneficial to manipulate rumen fermentation in vitro.