PURPOSE: To prepare the novel antibiotic substance, SI-4228B useful as an agricultural, horticultural or industrial fungicide, by culturing microorganisms belonging to Streptomyces genus.

CONSTITUTION: Microorganisms belonging to Streptomyces genus and capable of producing the antibiotic substance, SI-4228B, e.g. Streptomyces sp. SI-4228 strain (FERM-P No.6198), are inoculated in a nutrient medium, and cultured at 28W 32°C for 3W10 days under aerobic condition. The novel antibiotic substance, SI-4228 is separated mainly from the culture liquid, and is used as a fungicide for gray mold, anthracnose, sheath blight, rice blast, etc.