In taxonomic studies on two streptomyces, the strain MCRL-0357 which produces the antibiotic BD-12 was recognized to be a new species of streptomyces and named Streptomyces luteocolor nov. sp. The strain MCRL-0358 which produces antibiotic BY-81 was concluded to be a new variety of Streptomyces olivoreticuli Arai et al. The production of both antibiotics were described. In the course of screening antibiotics, two basic antibiotics, tentatively named BD-12 and BY-81, were found. These antibiotics were not identical with any other known antibiotics and seemed to be closely related to each other chemically. Antibiotics BD-12 and BY-81 were produced by the strains indexed as MCRL-0357 and MCRL-0358 respectively. These strains belong to the Genus Streptomyces, and, according to the classification proposed by Pridham et al.1), the strain MCRL-0357 may be classified into Rectus-Flexibilis, the Yellow series of streptomyces and the strain MCRL-0358 to Biverticillus, the Olive-buff series. The former was not identical with any streptomyces species previously described and, therefore, was named Streptomyces luteocolor nov. sp., while the latter was determined to be a new variety of S. olivoreticuli Arai et al.2). The present paper concerns the taxonomic study on both strains and also deals with the production of the antibiotics. Isolation, purification and properties of the antibiotics BD-12 and BY-81 will be reported in the succeeding paper.3)