We attempted to show the evolution of the magma and the geochemical characteristics of dikes and dike swarms by using the petrographic and geochemical data from 287 dikes, SE Korea. The dikes can be divided into mafic, intermediate, and felsic dikes in the field. And each of them is subdivided into three groups, two groups, and two groups, respectively. The group (I) among the mafic dikes most pervasively occurs and are distributed in both sides of the Yeonil Tectonic Line (YIL), which petrographic and geochemical characteristics are the same. These facts thus, strongly support the results of the previous studies which showed that they were intruded contemporaneously and that YTL was a main tectonic line which restricted the crustal clockwise rotation during the Early Miocene. The geochemical characteristics are discriminated according to the seven groups divided petrographically. The mafic, intermediate and felsic dikes belong to basalt and basaltic andesite, andesite and facile, and rhyolite, respectively, and the magmas mostly belong to calc-alkaline series. The geochemical data indicate that there were the fractional crystallizations of olivine, clinopyroxene, and plagioclase in the mafic dikes. And the content of characteristic elements and tectonic discrimination diagrams show that the dikes were formed from the magma related to the subduction of plate and that the tectonic setting was related to orogenic volcanic arc.