An in vitro gas production technique was used to evaluate the effect of propionic acid (10 mM) on six diets i.e. high (80R:20C), medium (50R:50C) and low (20R:80C) fiber sorghum diet (HFSD, MFSD and LFSD) and berseem diets (HFBD, MFBD and LFBD). Experimental results indicate that DMD either not affected due to propionic acid supplementation or increased (3.3%, 1.6%, 1.7% and 3.9% in MFSD, HFBD, MFBD and LFBD) slightly in some of diets. Methane production(mM/gDM) did not differ significantly due to 10 mM propionic acid supplementation, however, it was decreased 12.4% and 5.4% in HFBD and LFBD, respectively, when expressed in ml/gm DDM. Partition factor value was unaffected by propionic acid supplementation in almost all type of diets except MFSD, where it was increased by 11.2%. Microbial biomass (MBM) yield highest increased up to 23.5% in MFSD than 4.0% in HFBD and 5.3% in LFBD. TVFA (mM/100ml) increased significantly in all type of diets. A significant increase in propionic acid concentration (mM/100ml) was also seen in all the six type of diets. It was concluded from the results that propionic acid supplementation in sorghum and berseem containing diets decreased the methane production from 5.4 to 12.4% and significantly increasing propionate production without affecting the fiber digestibility. 1333019259.php