The present study was carried out to evaluate the effect of methanolic extracts of three plants, mehandi (Lawsonia inermis), jaiphal (Myristica fragrans) and green chili (Capsicum annuum) on methanogenesis, rumen fermentation and fermentation kinetic parameters by in vitro gas production techniques. Single dose of each plant extract (1 ml / 30 ml buffered rumen fluid) and two sorghum fodder containing diets (high and low fiber diets) were used for evaluating the effect on methanogenesis and rumen fermentation pattern, while sequential incubations (0, 1, 2, 3, 6 9, 12, 24, 36, 48, 60, 72 and 96 h) were carried out for gas production kinetics. Results showed that methane production was reduced, ammonia nitrogen was increased significantly, while no significant effect was found on pH and protozoal population following addition of different plant extracts in both diets except mehandi. Green chili significantly reduced digestibility of dry matter, total fatty acid and acetate concentration at incubation with sorghum based high and low fiber diets. Among all treatments, green chili increased potential gas production, while jaiphal decreased the gas production rate constant significantly. The present results demonstrate that methanolic extracts of different plants are promising rumen modifying agents. They have the potential to modulate the methane production, potential gas production, gas production rate constant, dry matter digestibility and microbial biomass synthesis.