Abstract: Two hundred and six cases aged ftom newborn to 50 years old of coronary arteries were studied with light and eledtron microscope. Special attention was paid to a lesion called focal intimal lysis. The authors emphasized that this lesion is a typical precursor of atherosclerosis （AS） because the site of the lesion was correlated well with that of AS, and a tendency of transition from the lesion to AS plaque was noted morphologically. The incidence, sites frequentiy involved, and the machanism of the lesion, its relation to AS were also studied.