The present invention provides an inhibitor of decrease in body temperature which comprises at lease one kind of an amino acid(s) selected from the group consisting of valine, asparatic acid, glycine and cystein as an active substance. This inhibitor of decrease in body temperature can inhibit the decrease in body temperature caused by general anesthesia and the like, and prevent and/or improve complications accompanied with the decrease in body temperature. It is preferable that the inhibitor of decrease in body temperature contain