Studies of hybridization among interfertile oaks (Quercus, Fagaceae) help us understand the interspecific limits and evolutionary implications pertaining to these species. However, in East Asia, little attention has been paid to introgression and hybridization, especially in relation to evergreen oaks. Our objective was to examine the natural hybridization and introgression among related taxa. We performed a genetics analysis of 158 individuals from three evergreen Quercus species in Korea (Q. acuta, Q. salicina, and Q. glauca). Focusing on six microsatellite loci, we investigated the typical morphological characteristics of each species. Bayesian admixture analyses and measures of genetic differentiation (F_ST R_ST G_ST, and G'_ST) were conducted. A feasible level of coincidence was found between the morphological classification and genotype of each individual, and the differentiation was significant between all pairings. However, six individuals showed mixed genotypes with other clusters, implying that they are putative hybrids. Our results suggest that these mixed genotypes among morphologically pure individuals might have arisen from backcrosses between a hybrid and one of the parental species.