In the course of our screening for new antibiotics, a new compound, viridomycin F (1, Fig. 1), was isolated from a culture broth of Streptomyces sp. K96-0188. Compound 1 is a complex of iron and p-substituted o-nitrosophenol trimer and showed moderate insecticidal and nematocidal activities. Several iron complexes of p-substituted o-nitrosophenols, viridomycin A (2)¹⁻³) and E⁴), actinoviridin (3)⁵), 4-hydroxy-3-nitrosobenzamide ferrous chelate (4)⁶), and ferroverdin (5)⁷⁸), have been isolated as green pigments from actinomycetes. As for biological activities, only moderate antibacterial activity of 2 against some Gram-positive bacteria has been reported¹³). In this report, we describe the characteristics of the producing strain and the fermentation, isolation, physico-chemical properties, structure elucidation, and biological activities of 1.