Quercetin is a flavonoid and is abundant in the plant kingdom. Green nanoparticles (gold and silver) were synthesized by using quercetin as a reductant via a green route for their potential nanoarchitechtonic applications. There were no toxic chemicals involved during the synthesis. The gold and silver nanoparticles exhibited surface plasmon resonance at 527 nm and 401 nm, respectively. Both nanoparticle solutions retained excellent colloidal shelf stability for 7 days and in cell culture medium. The crystal structure of the nanoparticles was observed by X-ray diffraction analysis. Field emission transmission electron microscopy images revealed that spherical nanoparticles were synthesized, with an average size of 20.2±4.8 nm for gold nanoparticles and 32.4±14.0 nm for silver nanoparticles. Observation of clear lattice fringes in the microscopic images suggested that both types of nanoparticles possessed a face-centered cubic structure. Catalytic activity was evaluated with respect to 4-nitrophenol reduction and methyl orange degradation. When increasing the amount of gold or silver nanoparticles used as a catalyst, the rate constant of the catalytic reaction was also increased. Cytotoxicity assessment on cancer cells demonstrated that both types of nanoparticles can be appropriate candidates for delivery vehicles of biologically active molecules, such as anticancer agents.