The genetic variability of two consecutive generations of a new strain of Crassostrea gigas, intended to be established in the Gulf of California, was evaluated at six microsatellite loci. A total of 66 alleles and 146 genotypes in the broodstock sample and 68 alleles and 168 genotypes in the F1 sample were detected. The mean observed heterozigosity was 0,65 for the broodstock and 0,67 for F1, with no significant differences between them. All loci showed a deficit of heterozygotes with the exception of ucdCg10 in the F1, but no evidence of cumulate inbreeding was found. Five loci demonstrated differences in allelic and genotypic frequencies. The monitoring of the genetic variability in hatchery-produced organisms is not a current routine task in the quality control process of most hatcheries. Microsatellite analysis is a good tool for monitoring the heterozygosity fluctuations along the productive life of cultured strains.