We examined the genetic variation within the species, the patterns of genetic diversty between populations, thermostability variations of enzymes and temperature tolerances of Corbicula japonica from the two main rivers In Korea. Starch gel electrophoresis was used to examine the genetic variation of 22 locl. Henting experiments of electrophoresis under the condition of 40$pm$5$^{circ}$ for 15$pm$5 min disclose thermostabllity differences, called heat-sensitive and heat-resistant types, within each 디ectrophoretic allozyme. Genetic diversity at the natural species level was high (77.3%), whereas the extent of heat-treat groups was relatively low (52.6%). The genetic diversity trends to decrease from the source of two main siderable high genetic diversity compared with a mean value of C. japonica species, It is recommended that several populations of the species in Korea should be preserved.