Abstract: The biometry, biomass production, density and the sex ratio of two edible venerid clams, Paphia malabarica and Meretrix casta and the hydrologic parameters of the clam beds of Ashtamudi Estuary were monitored for one year. The results of the study indicated that the density and distribution of these clams were influenced by salinity. The largest Paphia clams were obtained in November and the Meretrix clams in April. In P.malabarica the tissue mass production increased from July to December and in M.casta from April to December. In both species the male and female sex ratio was found to be 1:1. The P.malabarica was denser than M.casta in the estuary. Increased biomass production, percentage edibility and nutritional values were recorded highest during the monsoon season (June-September) indicating the best time for harvest to keep the fishery sustainable.