In May of 2009, 28 full-sib families were established by selecting mature breeders in the third generation selected line. Growth performances of the families were compared on the basis of shell height and shell length at juvenile and adult stages. Four families were randomly sampled from the 28 families and their genetic variation was evaluated by using seven microsatellite markers. Significant differences in mean shell length and height among the families were observed at days 110 and 320. A total of 23 alleles were detected at seven microsatellite loci in the four families and the number of the alleles at each locus ranged from 2 to 4, with an average of 3.3. The average observed (Ho) and expected (He) heterozygosity of the four families varied from 0.476 to 0.573 and from 0.584 to 0.679, respectively. The results of the analysis of molecular variance (AMOVA) indicated that 88.4% of the total variations was attributed to the genetic variations within family, whereas only 11.6% variations among families. The results that there exists highly genetic diversity and genetic differentiation among the four families indicates desirable conditions for developing superior lines of the species by family mating. Key words: Pinctada martensii, families, growth performance, genetic variation.