The present study was carried out with the objectives to evaluate the effect of different plant parts on methane production as rumen fermentation modulators and gas production kinetics by using in vitro gas production technique. Garlic (Allium sativum, T1) Eucalyptus (Eucalyptus globules, T2) and Neem (Azadiracta indica, T3) plant part powders were used for the evaluation for their inhibitory action on methane production, rumen fermentation and gas production kinetics on three type of wheat straw based diets i.e. high fiber diet (HFD), medium fiber diet (MFD) and low fiber diet (LFD). Methane was estimated by Gas Chromatography and results indicated that the maximum (51.96%) methane reduction was found on the supplementation of garlic powder in HFD as compared to that of control diet. Partition factor, microbial biomass, acetate to propionate ratio and gas production (b) was increased due to the addition of garlic powder. Garlic powder also showed the significant (P≤0.05) reduction in protozoa number in all type of diets. 1343455597.php