A total of 24 Colletotrichum isolates were isolated from diseased Japanese plum (Prunus salicina) fruits showing chlorotic regions with whitish-brown sunken necrotic lesions and phylogenetic relationships among the collected Colletotrichum isolates were determined. A subset of 11 isolates was chosen for further taxonomic study based on morphology and molecular characteristics identified using the internal transcribed spacer (ITS) and beta-tubulin (TUB2) genes. Isolates in the C. acutatum complex were analyzed using partial sequencing of five gene regions (ITS, GAPDH, ACT, TUB2, and CHS), and C. gloeosporioides sensu lato (s.l.) isolates were analyzed using seven gene regions (ITS, TUB2, GAPDH, ACT, CAL, CHS-1, and ApMat). Morphological assessments in combination with phylogenetic analysis delineated four species of Colletotrichum including C. gloeosporioides sensu stricto (s.s.), C. nymphaeae, C. foriniae, and C. siamense; these data identify Colletotrichum fioriniae and C. siamense two new species associated with plum anthracnose in South Korea. Finally, the pathogenicity of these four species in the development of plum anthracnose in South Korea was confirmed by inoculations of plum fruit.