The present invention provides a method for efficiently producing a β-alanyl-amino acid (e.g., carnosine) or derivative thereof. Specifically, it provides a method for producing a β-alanyl-amino acid (e.g., β-alanyl-histidine) or derivative thereof, by reacting a β-alanyl ester or a β-alanyl amide and an amino acid or derivative thereof in the presence of an enzyme or an enzyme-containing product that has an ability to form the β-alanyl-amino acid (e.g., β-alanyl-histidine) or derivative thereof from the β-alanyl ester or the β-alanyl amide and the amino acid (e.g., histidine) or derivative thereof. The present invention also provides a protein which is able to catalyze production of a β-alanyl-amino acid or derivative thereof from a β-alanyl ester or a β-alanyl amide and an amino acid or derivative thereof, and a polynucleotide encoding said protein.