Nanocomposite films of poly(ethylene terephthalate)(PET) and nano titania($TiO_2$) were prepared by melt compounding with a twin-screw extruder followed by hot pressing for the purpose of investigating antibacterial activity. FE-SEM, EDS and XRD measurements confirmed that nano $TiO_2$ was successfully dispersed at the level of individual particles in the PET matrix. Silver was introduced through photocatalytic reduction by nano $TiO_2$ under UV (254 nm) irradiation to the nanocomposite films after being immersed in aqueous solution $AgNO_3$ (100 ppm Ag ion). Even at 1 wt% of $TiO_2$ content, the nanocomposite with silver photodeposition exhibited strong antimicrobial activity against Klebsiella pneumoniae and Staphylococcus aureus in measurement by shaking flask method.