NOVELTY - Method of using Clostridium tyrobutyricum for fermenting bagasse hydrolyzates to produce butyric acid, involves culturing C.tyrobutyricum using medium containing 50 mg/mL of sodium butyrate followed by anaerobic bottle containing 50 mL of growth medium, obtaining fermentation stock culture, culturing the bacteria until concentration of thallus reaches 6-10 g/L, adding expanded culture solution to fiber bed bioreactor, transferring the culture solution to bagasse hydrolyzate, performing batch fermentation and obtaining butyric acid.    USE - The method is useful for culturing C.tyrobutyricum for fermenting bagasse hydrolyzate to produce butyric acid.    ADVANTAGE - The method is easy as bagasse hydrolyzate is used as carbon source and fiber bed bioreactor is used to perform immobilization fermentation, and increases productivity and yield of butyric acid. The butyric acid can be produced cost-effectively as agricultural waste is used as raw material.    DETAILED DESCRIPTION - Method of using Clostridium tyrobutyricum for fermenting bagasse hydrolyzates to produce butyric acid, involves (a) obtaining bacterial liquid of C.tyrobutyricum using inoculating needle, marking a line on strengthening medium containing 50 mg/mL of sodium butyrate and culturing the bacteria for 72 hours under 37 degrees C, (b) inoculating the single bacterial colony on the plate into 100 mL anaerobic bottle containing 50 mL of growth medium and culturing for 72 hours and obtaining first seed culture, (c) obtaining 1 mL of first seed culture to inoculate into 100 mL anaerobic bottle containing 50 mL of growth medium to cultivate for 72 hours and obtaining secondary seed culture which is used as fermenting stock culture, (d) obtaining 3 mL of fermenting stock culture to inoculate into 500 mL anaerobic bottle containing 100 mL of growth medium to cultivate for 48 hours and then into 5 L fermentation tank containing 2 mL of growth medium to expand culture for 24 hours such that the concentration of the thallus reaches 6-10 g/L, adding the expanded culture solution to fiber bed bioreactor through peristaltic pump at a speed of 60-100 mL/minute, repeating the process, when the free thallus concentration is reduced to 1-3 g/L, transferring the culture solution to bagasse hydrolyzate, performing batch fermentation using fermentation medium and feed supplement, repeating batch fermentation and obtaining butyric acid. The fermentation process is carried out at 150 rotations/minute and 37 degrees C using 6 mol/L sodium hydroxide of pH 6. The content of the bagasse hydrolyzate fermentation medium comprises (in g/l): total sugar (70), yeast extract (5), peptone (5), ammonium sulfate (3), potassium hydrogen phosphate (1.5), magnesium sulfate heptahydrate (0.6), and ferrous sulfate heptahydrate (0.03). The total sugar is prepared using bagasse hydrolyzate, where the preparation method for bagasse hydrolyzate involves mixing dried bagasse and 0.3 mol/L of sulfuric acid in a mass ratio of 1:10, hydrolyzing the mixture for 30 minutes under 121 degrees C, filtering and centrifuging the mixture, obtaining the supernatant and adjusting the pH to 6. The strengthening medium is prepared by adding 50 mg/mL of sodium butyrate in growth medium under 37 degrees C and pH 6 under anaerobic environment.