PURPOSE: A rice hull fermentation method, and a feed additive composition containing thereof are provided to effectively decompose and use low degradable carbohydrate inside rice hull. CONSTITUTION: A rice hull fermentation method comprises a step of injecting microorganisms in rice hull for fermenting. The microorganisms are selected from Lactococcus lactis or paenibacillus polymyxa. The fermentation process uses the rice hull as a carbon source. A feed additive composition contains the product obtained from the rice hull fermentation method.