In a previous paper, we reported that Streptomyces oganonensis No. Y-G 19Z produced oganomycin G when 5-mercapto-1-methyl-1H-tetrazole was added to the fermenting broth. During fermentation studies on oganomycin G, we discovered a new cephamycin-type antibiotic named oganomycin A, whose structure was determined to be 7S-(D-5-amino-5-carboxyvaleramido)-7α-methoxy-3-(p-sulfooxycinnamoyloxymethyl)-Δ³-cephem-4-carboxylic acid via spectrometric and degradation studies. Production of oganomycin A was significantly stimulated by the addition of p-hydroxycinnamic acid to the medium. Oganomycin A was converted to a glutaryl derivative (oganomycin GA) using D-amino acid oxidase from Trigonopsis variabilis IFO 0755. Hydrolyzing oganomycins A and GA with hydrochloric acid in moist acetone yielded oganomycins B and GB, respectively. Further chemical degradation studies confirmed the structure of oganomycin A: heating oganomycin A yielded p-sulfooxycinnamic acid sodium salt (V), which was converted to p-hydroxycinnamic acid (VI) upon treatment with hydrochloric acid, matching an authentic sample. Oganomycins A and B were found to be much more stable than cephamycins A and B, with less than 20% degradation over 24 hours at 29°C in pH 7.5 phosphate buffer, compared to over 70% degradation for cephamycins A and B.