Members of the family Tellinidae are considered major components of trophic chains in sheltered sandy beaches located in temperate and tropical waters, due to their high number of species and abundance, as well as their several ecological functions. The population dynamics and secondary production of two congeneric bivalves Tellina lineata and Tellina versicolor were assessed in a sheltered beach environment. Monthly samplings from December 2006 to February 2009 were carried out at Flexeiras beach in southeastern Brazil. Samplings were conducted according to a systematic design, where six transects (fixed 20 m apart) were established, each with 10 equally spaced sampling levels. From each level, a sampling unit (0.04 m²) was taken. The populations differed in several aspects as follows: (1) T. lineata showed a significant preference for occupying the intermediate levels of the beach, whereas T. versicolor showed higher densities at lower levels, (2) T. lineata had significantly higher density, grew significantly slower, the mortality rate was lower and the biomass (B), secondary production (P) and turnover rates (P/B) were higher than for T. versicolor. The differences in population parameters of the two species may be associated a difference in the species' capacities to use resources available in the marine environment.