A new spirotetronate-class polyketide, maklamicin (1), was isolated from the culture extract of an endophytic actinomycete of the genus Micromonospora. The structure and relative configuration of 1 were elucidated by interpretation of NMR and other spectroscopic data, and the absolute configuration was determined using the modified Mosher method. Maklamicin (1) showed strong to modest antimicrobial activity against Gram-positive bacteria.