In order to improve the phenotypic characters of cow strain of Manila clam Ruditapes philippinarum, hybridization and inbreeding effects of this strain were investigated between two generations by establishing inbreeding groups(F₂₂,F₃₃),hybrid groups(F₂₃,F₃₂)and control groups(C₂₂,C₃₃)with the parent of full-sib F₁ and F₂ (the upselection rate 10%),in July 2010.The results showed that the growth character and survival rate of larvae were partially improved,whereas the juveniles growth character was not increased by hybridization.The little growth heterosis was observed on larvae(0.95±1.23);the heterosis of larvae for F₂₃ was(0.36±0.59),that of F₃₂ was(1.56±1.96).The survival respectively was observed on juveniles(-2.90±3.20),the respectively of juveniles for F₂₃was(-4.60±3.21),that of F₃₂ was(-0.75±10.13).The midparent survival rate of larvae and juvenile were(9.43±4.41)and(8.66±12.25);the survival rate for F₂₃ were(0.77±3.60) and (6.70±8.81),that of F₃₂ were (20.93±7.92) and (10.94±16.28).The mating strategy was the major factor for hybrid effects during the larval period,then the maternal effect became the major factor for that during juvenile period.Growth of two generations was improved by inbreeding,but the survival rate of two generations was inbreeding depression.Generations F₂₂,F₃₃ were inbreeding depression on larvae,inbreeding depression rates of growth were(5.17±4.38)and(4.99±2.72);juveniles period of growth did not show inbreeding depression,inbreeding depression rates were(-0.79±13.66)and(-0.93±12.85).The inbreeding depression rate of survival for F₂₂ was(0.16±5.82) and (9.98±10.04) between larvae and juvenile,then these of F₃₃ were (19.33±11.28) and (13.08±16.17) respectively.The generation effect was the major factor for inbreeding effects.The phenotypic characters of this strain were effectively improved by close combination of upselection,hybridization and inbreeding.