Background and Aim : In recent years, the prevalence of infectious diseases has increased dueto the presence of multidrug-resistant pathogens, and the development of novel drugs is attractedmore attention for the treatment of infectious diseases. Nanotechnology has emerged as a potentarea in the introduction of novel antibiotics. Among the metallic nanoparticles, there is impressiveinterest in the antibacterial activity of silver nanoparticles (AgNPs) against diversemicroorganisms. Green synthesis of AgNPs has been studied with different biological sources asan alternative to chemical synthesis.Methods : This study aims to synthesize AgNPs in the presence of carrageenan polymer andinvestigate its antibacterial properties. For this purpose, nanoparticles were synthesized by asimple one-step method with ۰.۳% carrageenan solution and ۰.۰۱ M silver nitrate solution at ۶۰C for ۱ h. The characterization was performed by dynamic light scattering (DLS) after ۲۰, ۴۰,and ۶۰ min of the synthesis process to measure particle size and polydispersity index (PDI) andFourier transform infrared spectroscopy (FTIR) methods to investigate surface chemical groups.Finally, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration(MBC) of NPs were evaluated on Gram-positive (Staphylococcus aureus) and Gram-negative(Escherichia coli) bacterial strains.Results : The characterization results showed that carrageenan coated-AgNPs had a hydrodynamicdiameter of ۲۷۷.۱۲±۴.۷ nm and a PDI of ۰.۳۳۶±۰.۰۰۲ after ۲۰ min. FTIR analysis was performedto investigate the functional groups on the surface of the nanoparticles and it was confirmed thatfunctional groups in carrageenan are involved in the synthesis and stability of AgNPs. The brothmicrodilution method was applied to Staphylococcus aureus and Escherichia coli to determineMIC and MBC. The results showed that the MIC and MBC were ۱۴.۶ μg/mL and ۲۹.۳ μg/mL forE.coli and ۵۸.۶ μg/mL and ۱۱۷.۲ μg/mL for S. aureus, respectively.Conclusion : This study indicates that carrageenan coated-AgNPs exhibit strong antibacterialactivity against both gram-positive and gram-negative bacteria and might be administrated for thetreatment of infectious diseases.