The Kumamoto oyster () is an important wild oyster resource in Southeast Asia, including China, Japan and Korean. They are not only distributed naturally in China, but also live in abundance over a wide geographical distribution, ranging from Jiangsu to Guangxi, and Hainan Island. Traditionally, this species is a wild fishery resource; farmers capture these oysters from the reef or stone on the inter-tidal zone. Although the artificial breeding of this oyster was successfully conducted, but no relative information for genetic improvement was found. Selective breeding is the genetic manipulation of a cultured species for the purpose of improving specific traits of interest to humans. A variety of approaches have been taken in the study of the genetic breeding of mollusks, including Mendelian genetics, quantitative genetics, and cytogenetic and molecular genetic studies. However, not all of these approaches have contributed equally to the immediate development of genetically improved strains. Classically, population selection indicates the method of selection for the offspring bred by free mating among individuals with superior phenotypic traits in the majority from populations of original species according to the selective breeding objective via a comparison and appraisal between the original species and local species. Due to its simple operation and easy promotion, it has been widely used in the improvement of plant and animal species. Through continuous population selection, better cultivated species with rapid growth, strong stress resistance, high meat rate and high yield can be obtained. To improve the growth trait, response to selection and realized heritability for shell height was evaluated using the many radial rib line (Stock M: a number of ribs of left shell≥6) and the non-radial rib line (Stock N: a number of ribs of left shell=0) of the cultchless Kumamoto oyster in southern China. The shell height of Kumamoto oyster was considered to be a growth characteristic due to the positive association between shell height and yield. Truncation selection was conducted by selecting the largest 10% oyster from two stocks as parents for selected groups, while the equal number parents were randomly chosen as control groups before the removal of parents for truncation selection. Progeny from four groups were cultured the identical environmental conditions at larvae, spat and grow-out stage. Genetic index increased with oyster growth, strain M showed slightly higher response to selection and realized heritability than strain N during the whole history life. For strain M, response to selection and realized heritability were 0.33±0.04, 0.19±0.02 for larvae, 0.46±0.03, 0.26±0.02 for spat, and 0.63±0.11, 0.36±0.07 for grow out stage, respectively. The response to selection and realized heritability of Strain N were 0.30±0.04, 0.17±0.02 for larvae, 0.43±0.03, 0.25±0.02 for spat, and 0.58±0.10, 0.33±0.06 for growing out stage, respectively. At the end of 360 day, current genetic gain was 8.41% for Strain M, 7.71% for Strain N, respectively. The relatively high realized heritability has been obtained from the two strains, suggesting that there existed a degree of genetic variation between selective and control lines of this species. Our results clearly demonstrate that population selection can effectively improve growth trait and it is a promising way to Kumamoto oyster aquaculture.