Provided are a carnosine dipeptidase 1 inhibitor composition, a use for a material that inhibits carnosine dipeptidase 1, and a method for inhibiting carnosine dipeptidase 1. The present invention demonstrates the discovery of a plant- or animal-derived peptide exhibiting an inhibitory activity against carnosine dipeptidase 1, and thus, provides a novel and effective means that contributes to the prevention or amelioration of a cognitive function decline or the like.