Ruminants are given substantial quantities of concentrate diets full of quickly fermentable carbohydrates to increase output performance; however, it can also lead to digestive disorders. This study aimed to investigate the effect of adding NaCHO3 to a high-concentrate diet on the nutrient digestibility of locally available fibrous feedstuffs in the Philippines. The experiment utilized a rumen-fistulated Brahman bull. The treatment diets were the following: Treatment 1 (T1): Untreated rice (Oryza sativa L.) straw; T2: Urea-treated rice straw; T3: Napier grass (Pennisetum purpureum Schumach); T4: Napier silage; T5: Sugar cane (Saccharum officinarum L.) tops; and T6: Cogon grass (Imperata cylindrica L.). The nylon bags containing the treatment diets were incubated in the rumen at two periods: first at a high-concentrate (70% level), and second at a high concentrate added with NaCHO3). The results showed that the nutrient digestibility of locally-available feedstuffs varies significantly (p<0.05) both with and without NaHCO3. The addition of NaHCO3 in a high-fiber diet improves the digestibility of locally available fibrous feedstuffs in terms of dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF). Therefore, the addition of NaHCO3 to a high-concentrate diet has the potential to positively stabilize rumen pH and enhance the nutrient digestibility of locally available fibrous feedstuffs.