<jats:title>Abstract</jats:title><jats:p><jats:italic>Streptomyces triostinicus</jats:italic> produces triostin A, an antitumor antibiotic, as its major secondary metabolite. Surprisingly, this strain also produced a trace amount of echinomycin. We sequenced the entire triostin A biosynthetic gene cluster from <jats:italic>S. triostinicus</jats:italic>, and found that this 36 kilobase‐long gene cluster contained an ORF homologous to <jats:italic>ecm18</jats:italic> that encodes a thioacetal‐forming enzyme responsible for the triostin A‐to‐echinomycin bioconversion. These findings indicate that, unlike previously thought, <jats:italic>S. triostinicus</jats:italic> is capable of producing not only triostin A but also echinomycin. Our observation suggests potential value in careful re‐analysis for metabolites from previously characterized natural product producers with the current technologies.