The present study was conducted in order to investigate the effects of Yucca Schidigera extract (YSE) at 25, 50 and 100 µl /75 ml culture ruminal fluid on in vitro ruminal fermentation characteristics, diet degradability and methane production using the semi-automatic system for gas production (GP) assay. Three rumen-cannulated Barki sheep (58.0 ± 2.3 kg of BW) were used as inoculum donors. The culture fluid was anaerobically incubated with 300 mg of a mixture of concentrate and peanuts hay (50:50, w/w) at 39ºC for 24 h. Three runs of GP were used for each assay. Results showed that YSE addition to the diets decreased GP (P<0.05) than those obtained by the control. Compared with the control, CH₄ production and NH₃-N concentration were decreased by 37 and 18.5% with 25 µl YSE. Truly degraded dry matter (TDDM) was similar among the different levels of YSE addition. While truly degraded organic matter (TDOM) was decreased (P < 0.05) by 100 µl YSE addition but there were no differences among 25 and 50 µl levels of YSE addition. Ruminal acetate proportion was lower (P < 0.05) with 100 µl YSE compared with the control. Acetate to propionate ratio tended to decrease (P = 0.091) with the addition of YSE. Total rumen protozoal number increased (P< 0.05) by 50 µl YSE while decreased by 25 and 100 µl YSE addition. The results indicated that YSE exhibited a strong suppressing effect on ruminal methanogenesis, NH₃-N concentrations and protozoal populations which could modify the rumen fermentation patterns may be a beneficial ruminal modifier for improving nutrient utilization and animal performance.