Hybridized families of bay scallop Argopecten irrandians irradians between Stock A and Stock B, which are separated from each other were established by using the pair mating and self..fertilized families were used as control groups at the spring of 2002. The experiments consisted of AA ( A .. .. A .. ) , BB( B .. .. B .. ) , AB( A .. .. B .. ) and BA ( B .. .. A .. ) groups. Heterosis is very clear. Growth and survival of the hybrid progeny are both improved. Considering growth, heterosis is 35. 34 % at larvae stage and 21. 17 % during grow out , respectively. The growth rate of the cross compared with the self..fertilized was improved 35. 53 % for AB and 35. 13 % for BA at larvae stage, and which was 43. 32 % for AB and 12. 34 % for BA during grow out. Considering survival, heterosis is 35. 17 % at larvae stage and 12. 34 % during grow out , respectively. The survival percentage of the cross compared with the self..fertilized was improved 25. 23 % for AB and 12. 36 % for BA at larvae stage, and which was improved 49. 44 % for AB and 21. 29 % for BA during grow out . The genet ic difference between Stock A and Stock B may be the success fundament of genetic improvement.