Hydantocidin, a new compound with potent non-selective herbicidal activity, was found in a submerged culture of Streptomyces hygroscopicus SANK 63584. It was isolated from the culture filtrate by the following successive treatments comprised of activated carbon, Diaion HP-20, Dowex 50WX4, and Avicel column chromatographies. Finally it was crystallized as colorless needles from acetone. The molecular formula, C7H10N2O6, was determined by analyses of HRFAB mass spectrum in conjunction with 13C NMR spectrometry. The structural elucidation revealed that it has a unique structure with a spiro-bond between ribose and hydantoin moieties in the molecule. The characteristic herbicidal activities against annuals as well as perennials, including monocotyledonous and dicotyledonous weeds, were observed.