Effects of condensed tannins on methane, total gas and volatile fatty acid formation were explored for some forage legume species. There were significant differences between the legumes species as to condensed tannins (P < 0.01). The contents of condensed tannins of Coronilla orientalis(CO), Coronilla parviflora (CPW), Dorycnium pentaphyllum(DP), Arygrolobium(A), Lotus corniculatus Trabzon(LCT), Lotus langustissimus (LA) and Lotus corniculatus vartenofolius(LCV) were of 3.78, 103.78, 18.41, 0.75, 22.19, 55.58, and 8.97 mg/kg dry matter, respectively. Likewise, accumulated methane, carbon dioxide, and total gas volume (mL/1.0 g dry matter) at 144h for Lotus corniculatus vartenofolius (27.98 mL, 210.94 mL, 270.00 mL) were higher. Methane, carbon dioxide, and total gas volume (mL/1.0 g dry matter) at 144 h for Dorycnium pentaphyllum (15.07 mL, 132.00 mL, 190.50 mL) were lower (P < 0.05), respectively. The content of condensed tannins in legumes decreased total gas, methane, and carbon dioxide gas production for all forage legume species. There was no difference in total volatile fatty acid production, acetic acid, and propionic acid concentration, and pH for the rumen fermented fluid for all forage legumes species in the experimental period (144 h). However, there were differences in ammonia concentration, i-Butiric (i-B) n-Butiric(n-B) n-Valeric(n-V) i-Valeric(i-V), in the fermented fluid, and the acetate-to-propionate ratio was affected for all forage legumes (P < 0.01). Crude protein ranged, on average, from 13.2 to19.3% dry matter. The neutral detergent fiber and acid detergent lignin contents ranged from 33.17 to 46.64% dry matter and from 29.51 to 43.16% dry matter, respectively. The lowest values corresponded to Lotus corniculatus, and, the highest, to Dorycnium pentaphyllum, harvested at the flower stage. Results indicate that condensed tannin content on methane production can be decreased to indirect effects via reduced hydrogen production (and presumably reduced forage digestibility) and via direct inhibitory effects on methanogens.