Novel rifamycins characterized by the following structural formula ##STR1## WHEREIN Me represents a methyl group, n represents 3, 4, 5 or 6; g represents 0, 1 or 2; and each R represents a lower alkyl group selected from methyl or ethyl substituting for a hydrogen atom of a --CH.sub.2 -- group; and wherein, when g is 2, the two lower alkyl groups may replace hydrogen atoms of two different methylene groups as well as hydrogen atoms of the same methylene group. The compounds of this invention possess a broad spectrum antibacterial utility accompanied by a low toxicity.