In the course of screening for new antibiotics active against fungi, an actinomycete strain No. PI57-2 that had been isolated from a soil sample collected in Fiji Island was found to produce novel antibiotics, pradimicins A and B. Pradimicin A, the major component showed moderate in vitro activity against a wide variety of fungi and yeasts including clinically important pathogens. More interestingly, it exhibited marked in vivo therapeutic activity against systemic fungal infections caused by Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans strains in mice. Degradation studies revealed that pradimicin A has a unique structure containing the following moieties: D-Alanine, D-xylose, 4,6-dideoxy-4-methylamino-D-galactose and a substituted 5,6-dihydrobenzo[a]naphthacenequinone. This communication presents production, isolation, chemical and biological properties and structures of pradimicins A and B. Based on the taxonomic studies performed, strain PI57-2 is classified as a heretofore undescribed species of the genus Actinomadura and named Actinomadura hibisca sp. nov. (ATCC 53557), and the details will be reported in a separate paper.