Green synthesis of metal nanoparticles has been gaining great interest due to the increasing need for eco-friendly manufacturing and application of nanomaterials. Metal nanoparticles, especially silver nanoparticles, are widely used in water treatments and as environmental remedy. Here we present a method to synthesize silver nanoparticles at room temperature using green tea extract under visible light irradiation, along with an application for enhanced photocatalytic degradation on methylene blue (MB) dye. Ag nanoparticles were synthesized under different photoreduction times and then further characterized. The photocatalytic rate of synthesized nanoparticles was also investigated and compared with TiO₂ nanowires under UV and visible light irradiations. The results showed that Ag nanoparticles can directly degrade MB dye through plasmonic excitation and electron transferring under visible light, and Ag nanoparticles can further enhance TiO₂ photonic degradation by enhanced e-h separation with UV and/or a wide band light, including UV light. Ag nanoparticles under visible light photoreduction for 0.5 h presented better behavior for two kinds of plasmonic enhanced photodegradation; the average size of the nanoparticles is about 30 nm. Therefore, the green synthesized Ag nanoparticles exhibit promising prospects in chemical and biological pollutant treatment.