The minerals contained in rocks record physical and chemical information from the time when the rocks were formed. EPMA is useful for investigating the precise chemical composition and 2-dimensional distribution of the elements in these rock-forming minerals. Here, element mapping of plagioclase in lava from the Mt. Unzen volcano was carried out using a Shimadzu EPMA™ electron probe microanalyzer (EPMA-8050G). As a result, it was found that microscopic particles consisting of Mg and Fe existed in the rim area of the plagioclase, thus providing valuable information for understanding the history of interaction between phenocrysts and magma.