The antibacterial effects of methanol, ethanol, chloroform extracts and alcalase hydrolysis of Cerastoderma and Didacta were investigated against Salmonella typhi, Salmonella paratyphi and Staphylococcus aureus by disk diffusion method, Minimum Inhibitory Concentration and Minimum Bactericidal Concentration. Methanolic and ethanolic extracts of Cerastoderma showed the highest effects against S. typhi (20.33 ± 0.33 and 12.33 ± 0.33) and S. paratyphi (22.66 ± 1.45 and 15.33 ± 0.33), however, the same effects against S. aureus (18.00 ± 0.00 and 17.00 ± 0.00) were observed for two bivalves. Chloroform extract of Cerastoderma and Didacta showed similar effects in controlling S. paratyphi (8.00 ± 0.58 vs 10.00 ± 0.57) and S. aureus (16.00 ± 1.15 vs 16.00 ± 1.15) in concentrations of 10 and 5 mg ml^-1. Chloroform extract of Cerastoderma exhibited higher effect than that from Didacta against S. typhi (11.00 ± 1.73 vs 8.00 ± 0.58) and the dilution of 10 mg ml^-1 had the most suitable performance. The enzymatic hydrolysis of the Cerastoderma and Didacta showed the same performance in controlling of S. typhi (13.67 ± 4.37 vs 13.33 ± 1.76) and S. paratyphi (17.00 ± 0.58 vs 15.33 ± 1.45). However, the enzymatic hydrolysis of Cerastoderma showed better effect than that of Didacta in controlling S. aureus (18.00 ± 1.15 vs 13.00 ± 2.30), and the 10 and 5 mg ml^-1 dilutions were the most appropriate concentrations. It is concluded that Cerastoderma can be used as a resource with potent antibacterial compounds in the preparation of natural antimicrobial agents.