A new melanogenesis inhibitor, named amphistin, was isolated from the fermentation broth of an actinomycete strain KP-3052. Amphistin was purified from the culture filtrate by the combination of cation exchange, gel filtration, and aminosilyl silica gel chromatographic methods. The structure of amphistin was elucidated as gamma-(beta-histidinoalanino)homoalanine by NMR experiments including 1H-15N HMBC experiment and other spectroscopic analyses. Amphistin inhibited the melanogenesis of B16 melanoma cells at concentration of 6.8 microM.