Two new types of macrolide antibiotics, YM-32890 A and B, have been isolated from the fermentation broth of cytophaga sp. YL-02905S. In this paper, the taxonomy of the producing strain, fermentation, isolation, structure elucidation, and biological activity of the antibiotics are reported. YM-32890 A inhibits the growth of staphylococci including a macrolide-resistant strain, but shows no antimicrobial activity against other Gram-positive, Gram-negative bacteria and yeast.