PURPOSE: To obtain a microorganism protecting agent useful for preparing a frozen (freeze-dried) microorganism cell having a high survival ratio, reducing damage and death of the microorganism cell during freezing and freeze-drying, containing a mixture of specific amino acids and a mixture of their derivatives. CONSTITUTION: This microorganism protecting agent contains a mixture of at least three of aspartic acid, arginine, glutamic acid, proline, lysine, leucine and methionine or a mixture of their derivatives. A mixture of equal amounts of sodium aspartate, sodium glutamate and lysine hydrochloride is preferable.