The present invention relates to a method of improving storage stability of dried microorganisms, such as dried lactic acid bacteria, by allowing the dried microorganisms to coexist with an L-arginine acidic amino acid salt, a composition comprising dried microorganisms and an L-arginine acidic amino acid salt and a process for producing the same, and a method of storing dried microorganisms in the presence of an L-arginine acidic amino acid salt. The storage stability of dried microorganisms can be improved by allowing the dried microorganisms to coexist with an L-arginine acidic amino acid salt.