Abstract: The Manila clam(Ruditapes philippinarum),production of which was 4 million tons in 2015,is a kind of important economic shellfish in China.In order to improve the productivity traits of R.philippinarum,a mass selection program for faster growth was carried out.The shell length of the second generation of R.philippinarum breeding line were compared with the controls in larval and juvenile stage.Selection response(SR),realized heritability(h_R²),and genetic gain(GG)were also estimated.The average selection response,realized heritability and genetic gain were(0.516±0.297),(0.324±0.187),and(2.902±2.114)during larval stage,respectively and were(0.300±0.262),(0.188±0.164),and(9.463±8.418)during juvenile stage,respectively.It is concluded that mass selection is an effective approach to improving growth traits in the stocks of R.philippinarum.