A novel antibiotic complex, maridomycin, which is a lipophilic basic substance and mainly active against gram-positive bacteria, was obtained from the fermentation broth of Streptomyces hygroscopicus No. B-5050. Maridomycin was found to consist of six components, maridomycins I, II, III, IV, V and VI, which were isolated by silica gel adsorption or partition chromatography. The six components show only end absorption in UV-spectra and are classified as a new group of macrolide antibiotics from their physicochemical, chemical and biological properties. This paper deals with the isolation and characterization of maridomycin.