Based on mainly NMR spectral data, the structure of notonesomycin A, a novel macrolide antibiotic has been determined as shown in Fig. 1.Notonesomycin A is an antifungal antibiotic isolated from the mycelium of Streptomyces aminophilus subsp. notonesogenes 647-AVl and is effective in the treatment of sheath blight disease of rice plant in a green house test'). We wish to report herein the structural elucidation of notonesomycin A accomplished mainly by 'H and 13C NMR spectral analyses.