The present invention provides a safe and novel stabilizing agent for enzymes; a composition containing an enzyme and the stabilizing agent; and a kit containing the stabilizing agent composition. According to the invention, deactivation or inactivation of the activity of the enzyme during storage, drying, freezing, etc. can be prevented, without raising any problem of potential infection of an enzyme with a pathogen. For purposes of the invention, the stabilizing agent for an enzyme contains a plant-derived polypeptide as an active ingredient.