Two new tetracenedione derivatives, nocatriones A (1) and B (2), were discovered from the culture broth of a marine actinomycete, Nocardiopsis sp. KMF-002, which was isolated from the tissue of an unidentified dark purple marine sponge. The structures of 1 and 2, which are tetracenediones containing α-pyrone substituents, were determined to be 3,8,10,11-tetrahydroxy-2-(4-hydroxy-2-oxo-2H-pyran-6-yl)-1-methyltetracene-5,12-dione (1) and 3,8,10,12-tetrahydroxy-2-(4-hydroxy-2-oxo-2H-pyran-6-yl)-1-methyltetracene-6,11-dione (2). Ultraviolet B (UVB)-irradiated cells treated with 10 μM nocatrione A (1) significantly decreased the level of MMP-1, a protein that degrades collagen and other extracelluar matrix components that comprise dermal tissue, when compared to untreated cells. These results support that nocatriones A (1) and B (2) may show antiphotoaging activity in UVB-irradiated models.