A new compound, designated nectriatide (1), was isolated as a potentiator of amphotericin B (AmB) activity against Candida albicans from the culture broth of Nectriaceae sp. BF-0114. This structure was elucidated based on spectroscopic analyses (1D and 2D NMR data), chemical methods, and total synthesis. Compound 1 was a unique cyclotetrapeptide consisting of l-N-methyltyrosine, anthranilic acid, l-alanine, and l-valine. Compound 1 and several synthetic derivatives, including linear peptides, potentiated AmB activity against C. albicans by up to 16-fold (the MIC value of AmB decreased from 0.5 μg/mL to 0.031 μg/mL in combination with test compound).