A new aminoglycoside antibiotic, S-11-A, was isolated from the fermentation broth of the 2-deoxystreptamine negative (DOS-) mutant of Bacillus circulans S-11. The structure of S-11-A was elucidated as l-deamino-l-hydroxyxylostasin, which contains an intermediate of DOS biosynthesis (S-11-P) and has resistance to some aminoglycoside-inactivating enzymes. This is the first finding of antibiotic production by a DOS- mutant without any supplementation of DOS or a DOS analog, and could be described as a novel method of getting a new aminoglycoside antibiotic.