Silver nanoparticles are used in many industries due to their disinfection and antibacterial properties. Biological methods of nanoparticle synthesis have been suggested as possible ecofriendly alternatives to chemical and physical methods. In this study, biologically synthesized silver nanoparticles using Magnolia kobus leaf extract were coated on the surface of latex foam products using dip coating (exposure to nanoparticle solution) or ultrasonic treatment. SEM image of the treated foam showed that silver nanoparticles were uniformly coated on the surface of latex foam. Antibacterial properties were tested by counting viable Escherichia coli cells after 24 h growth in shake flask cultures containing latex foams coated with silver nanoparticles. Foams coated with silver nanoparticles showed higher antibacterial activities compared with foams untreated. Smaller silver nanoparticles synthesized at higher temperature showed higher antibacterial activity due to the larger specific surface area and higher content of silver nanoparticles. The growth of E. coli decreased with increasing the concentration of silver nanoparticles. Ultrasonic treatment showed higher adsorption and lower desorption of silver nanoparticles to and from the foams compared with dip coating, resulting in higher antibacterial activity.