The antibiotic substances are produced by strain of Streptomyces carcinomycicus (S-9) was isolated from soil of Brassica campestris Linn. crop field of Agra district. It was found to be strongly antagonistic to Alternaria brassicae (Berk.) and Alternaria brassicicola (Schw.) which causing the leaf spot disease of crucifers. Its growth characters on various media have been determined and organism placed in section and classification which identified as a strain of Streptomyces carcinomycicus on the basis of growth and biological characteristics. Streptomyces carcinomycicus strain is strongly antagonistic on agar medium produced active principle in liquid culture media. The culture filtrate inhibits the spore germination of Alternaria brassicae (Berk.) and Alternaria brassicicola (Schw.) on leaf. It is clear that the antifungal activity of culture filtrate decrease with increase in the storage time at all the temperatures. The antibiotic substance can be stored without any appreciable loss in its activity for 30 days at pH 6-8 and temperature 6⁰C. It is soluble n-butanol in, ethanol, isopropyl alcohol, benzene and toluene.