Given consideration is the study of ESR on the radical polymerization of vinyl or diene compounds, because ESR spectroscopy is a promising technique in acquiring information on the propagating radical. There had been attempted ESR measurements of the polymerization system, but since there exists no signal in these polymerizations in the liquid state, they were performed in their frozen states. However, in these times, observing the propagating radicals of diene compounds at room temperature by the aid of a computer is made possible. Presented in the paper is the well-resolved ESR spectra of the propagating radicals of diene compounds and described in the basic information on the addition mode in the radical polymerization of diene compounds.