A Streptomyces, No. 3668-L2, isolated from a soil sample taken from the campus of University of Tokyo produced an antibiotic which had properties similar to bottromycin discovered by Waisvisz et at¹. Acid hydrolysis of bottromycin have been known to yield valine, glycine, β-methylphenylalanine, β-2-thiazole-β-alanine and two unidentified ninhydrin-positive substances^{2, 3, 4)}. The similar amino acids and ninhydrin-positive substances were isolated from the hydrolysate of the antibiotic No. 3668-L2 and the two ninhydrin-positive substances were determined to be β,β-dimethyl-α-aminobutyric acid (DMAB) and ʟ-cis-3-methylproline. In another paper, the structural studies of the antibiotic No. 3668-L2 which was identified as bottromycin will be reported by Nakamura et al⁵⁾. Besides the amino acids described above, a small amount of ʟ-proline was isolated from a hydrolyzate of the antibiotic No. 3668-L2, and it suggested an existence of a small amount of another antibiotic. Actually, the antibiotic No. 3668-L2 was shown by a thinlayer chromatography to contain the main component which was identical with bottromycin and designated bottromycin A, and another minor component designated bottromycin B. Bottromycins A and B were separated and bottromycin B was suggested to have a similar structure to bottromycin A except L-proline moiety instead of ʟ-cis-3-methylproline. This paper presents characteristics of Streptomyces No. 3668-L2, isolation and properties of bottromycins A and B.