Pacific oyster, , is the most widely cultured oyster in the world. China produces more than 4.35 million tons of oysters annually. However, nearly all of the oyster broodstock in China remains unselected. This leads to many problems such as low growth rate, high mortality rate, and irregular shell shape. A selective breeding program is an effective way to resolve these problems, and Pacific oyster culturing would undoubtedly benefit from selective breeding for productivity traits such as rapid growth and high yield. Growth-related traits are of particular interest to farmers because of their economic importance. Color polymorphisms are relatively common in marine shellfish including , and consumers are willing to pay more for seafood with specific colors. During the period of 2010-2013, four successive generations of four shell-color families (white, black, golden, purple) were produced. None of the specifically colored lines showed superior productivity, and so truncation selections for shell height were initiated based on five fourth-generation black-shell and five fourth-generation white-shell families in 2014. Applying the same intensity of selection in the upward direction, two selected and two control lines were created. These lines were reared under the same environmental conditions at the larvae, spat, and grow-out stages. The progeny of the mass-selected lines were compared to those of controls in a 490-day farming experiment. Mean shell height and mean wet weight of the selected lines were significantly greater than those of the controls from day 120 onwards (<0.05). At harvest on day 490, the black-shell and white-shell oysters had mean shell height of (102.06±10.46) mm and (102.84±14.90) mm, respectively, and mean wet weight of (83.14±18.85) g and (84.46±16.98) g, respectively. The increase in shell height for selected blackshell oysters and white-shell oysters compared with that of the control was 9.04% and 9.01%, respectively, and the increase in wet weight was 9.33% and 10.50%, respectively. The estimated gain was consistent with the expected gain for mollusk species (10%-20% per generation). In the black-shell and white-shell mass-selected lines, the realized heritability of shell height was 0.353±0.093 and 0.405±0.111, respectively, the realized heritability of total weight was 0.297±0.12 and 0.377±0.190, respectively, the average selection response of shell height was 0.545±0.143 and 0.625±0.171, respectively, and the average selection response of total weight was 0.297±0.124 and 0.377±0.190, respectively. The total genetic gain of total weight for the black-shell and white-shell lines was (10.16±3.64)% and (11.34±1.94)%, respectively, indicating that total weight had improved markedly during selection for shell height. In conclusion, growth improvement for the two mass selected lines can be achieved by selecting the individuals with the greatest shell height. The relatively high realized heritability estimates obtained for the two mass-selected lines indicate that there is genetic variation in the two stocks, and that mass selection could be used to select for rapid growth in the next generations.