Rearing density is one of the important factors that strongly effect on growth rate, survival rate and rearing efficiency of many aquatic species as well as Ben Tre clams. This study presents the results on effects of four densities (3.000, 4.000, 5.000 and 6.000 individual/m2 in order to identify the suitable density for rearing this species in pond. The study was conducted from May to August, 2012 in brackish water pond belonged to Dong Minh village, Tien Hai district, Thai Binh province. Results showed that the clams reared at the density of 3,000 individual/m2 was highest of relative growth rate in length and weight (0. 92 percent/day and 1.59 percent/day, respectively (p0.05). There were no significant differences in relative growth rate in length and weight between the density of 4,000 individual/m2 (0.77 percent/day
1.43 percent/day) and 5000 individual/m2 (0.8 percent/day
1.46 percent/day) but there were significant differences when compared to those in density of 3,000 individual/m2 and 6,000 individual/m2. This clams reared at the densities of 3,000 individual/m2 was highest (92 percent) and lowest at density of 6,000 individual/m2 (88 percent). From this result, it could be suggested that the most suitable density for rearing the Ben Tre clams in pond should be less than 5,000 individual/m2 in order to optimize the growth, survival rate of seed.