In the course of searching for novel fungicidal antibiotics, a new tetramic acid-containing metabolite, A90931a, was isolated from Streptomyces sp., along with a second factor (A90931b) that was present in smaller quantities, recently described from Stenotrophomonas maltophilia, and known as maltophilin. Both are macrocyclic compounds with a tetramic acid residue and a tricyclic fused ring system, similar to the previously reported discodermide. Their structures were determined using spectroscopic data from the isolates and their acetylated products. A90931a was spectroscopically identical to the previously described antibiotic TAN-883b (whose structure was unreported) and very similar to catacandin B (another compound with an undetermined structure). A90931a and A90931b showed fungicidal activity against Plasmopara viticola, the causal agent of grape downy mildew—a devastating disease in commercial viticulture worldwide. Due to its similarity to maltophilin, A90931a was named dihydromaltophilin. This paper describes the isolation and structural characterization of dihydromaltophilin (A90931a).