The species delimitation of some members of Curvularia with 4-septate conidia was studied. Conidial shapes and sizes were variable to some extent depending on isolates and herbarium materials examined. By crossing experiments, C. affinis, C. fallax, and C. senegalensis showed no reproductive isolation from C. geniculata. Some isolates obtained from culture collections and from fields were not fertile with tester isolates of C. geniculata. Their conidial morphology were somewhat different from C. geniculata. SEM observations also revealed their morphological difference from C. geniculata. Restriction fragment length polymorphism (RFLP) of total DNA was analyzed with several isolates of species belonging to the “geniculata” group of genus Curvularia. DNA fingerprinting with probes prepared from GPD-1 and tublin coding regions gave clear differences among them, resulting in different banding positions. The results of analyses also confirmed that C. senegalensis, C. affinis, and C. fallax are synonymous to Curvularia geniculata. Two populations having 4-septate conidia with warping hilum and one population with rough surface conidia were clearly different from C. geniculata.