Abstract: Effects of gypenoside on ruminal fermentation were investigated by an in vitro gas technique on mixed rumen microorganisms collected from goats. Experiment 1 was conducted to assess effects on methane production and fermentation characteristics of rumen microorganisms. Experiment 2 was done to assay effects on fermentation kinetic parameters. The diet consisted of Leymus chinensis 0.42 g, ground corn grain 0.126 g and soybean meal 0.054 g(1 mm screen)as substrates in each fermentation vessel. Five different doses were used for each compound (0, 5, 10, 20 and 40 mg/60 mL of the total culture medium). Compared with the control, during an 8 h fermentation, methane concentrations were reduced by 30.20％, 43.49％, 44.67％ and 75.8％ respectively after gypenoside addition(P<0.05). During a 12 h fermentation, gypenoside reduced methane concentration by 6.97％, 9.63％, 18.90％ (P<0.05) and 61.82％ (P<0.01 ) respectively at the four gypenoside concentrations. During a 24 h fermentation, methane concentration decreased by 2.34％, 9.39％, 6.90％ and 20.73％ after gypenoside treatment. A significant linear pattern was observed between methane production and gypenoside dosage (P<0.01). The hydrogen utilization was lower than the control at the 10 mg level (P<0.01). The TVFA (total volatility fatty acid), acetate, propionate, isobutyrate acids, valerat, isovalerate and BCP concentrations were increased by the gypenoside treatments at the 10 mg level (P<0.05) while butyrate was reduced by gypenoside treatment at 40 mg (P<0.05). The acetate to propionate ratio increased significantly with 10 mg and 20 mg of gypenoside (P<0.05). There was a significant quadratic pattern for acetate, butyrate, isobutyrate, valerate, isovalerate, BCP, TVFA and acetate to propionate ratio and TVFA concentration with the increasing gypenoside dose (P<0.05 or P<0.01). There was also a linear pattern for butyrate (P<0.01). Relative to the control, the protozoa counts of treatment groups were significantly reduced by gypenoside addition (P<0.05 or P<0.01), and there were linear and quadratic patterns between protozoa numbers and saponin dosage (P<0.01). Microbe protein was not changed abruptly, but tended to increase. Ammonia nitrogen concentration was significantly higher than in the control at 10 and 40 mg of gypenoside supplementation, and there was a linear effect between ammonia concentration and gypenoside levels. The theoretical and actual gas production was reduced at high saponin levels, and there were significant linear and quadratic patterns between gas production and gypenoside levels. Significant linear and quadratic effects were observed on rate of gas production with increasing gypenoside levels. These results indicated that gypenoside addition can modify the microorganism fermentation pattern, reduce methane production, prompt VFA (volatility fatty acid) concentration, improve feed conversion efficiency and abate pollution of the environment by methane derived from ruminants.