The purpose of this work was to screen the actinobacteria having antimicrobial activity of fourteen strains of Streptomycetes which was isolated from the marine bivalves Meretrix casts (Gmelin) Parangipettai coastal region. Four isolates showed a strong activity against S. aureus. These isolates where extensively studied for their in vitro anti-microbial activity against Grampositive and Gram- negative bacteria. The results indicated that obtained isolates were highly active against S. aureus, E. coli, P. mirabilis and S. pyogenes in primary screening. The morphological, micromorphological, physiological and biochemical results obtained for the antibiotic producing strains were compared with those of the Streptomyces species given in the key of Nonomura (1974) and Berey’s Manul of Determinative Bacteriology (Buchanan and Gibbons, !974) and was identified four strains as Streptomyces orientials (PS-1), S. hastedii (PS- 2), S. nigellus (PS-3), and S. sclerotialus (PS-8). Hence it is suggested that the strains isolated and identified from the marine bivalve possessing antibiotic properties are worth investigating in details in future for isolating the antibiotics for human welfare.