During the course of our screening for new antibiotics, Micromonospora echinospora subsp. echinospora Y-03559J was found to produce a novel isonitrile compound, YM-47515 (1) along with a probable degradation product 2. The structure of 1 was assigned by spectroscopic analysis including 2D NMR and IR experiments. The relative stereochemistry of 1 was also proposed by comparison of spectral data with those of a closely related compound aerocyanidin (3). YM-47515 (1) showed promising antimicrobial activity against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA).