Fermentative characteristics and methane production of diets with high inclusion of Enterolobium schomburgkii and Senna occidentalis plants on a Brachiaria humidicola based diet were studied, using the semi-continuous ruminal fermentation system (Rusitec). The evaluated treatments were: T 1 -100% B. humidicola (Control); T 2 - 40% B. humidicola + 60% E. schomburgkii ; T 3 - 25% B. humidicola + 75% E. schomburgkii y T 4 - 25% B. humidicola + 75% S . occidentalis . In two evaluation periods of 10 days (7 adaptation and 3 analysis), gas production, methane, volatile fatty acids (VFA), ammonia, and dry matter and organic matter degradation were evaluated. The results showed that a high inclusion of E. schomburgkii reduced methane production by affecting organic matter degradation. Meanwhile, S. occidentalis increased diet degradation and ammonia, valerate, isobutyrate and TVFA levels, observing an average reduction of 29% in methane production. Several mechanisms may be determining the lower methane volumes observed with this species. Further studies to isolate and quantify the influence of the secondary metabolites present in these plants on ruminal methanogenesis are required.