Effects of silver nanoparticle (AgNP) and gold nanoparticle (AuNP) on photon upconversion based on sensitized triplet-triplet annihilation were examined in the system of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA). The ITO electrodes immobilized with AgNPs and AuNPs were prepared by electrophoretic method. Samples were prepared by sandwiching the solution of PtOEP and DPA between glass and the ITO electrode modified with AgNPs or AuNPs. In the sandwich samples, the enhancements of upconversion fluorescence from DPA were observed in the presence of AgNP, while the quenching of the upconversion fluorescence in the presence of AuNPs. The enhancements are most likely attributable to large electric fields due to localized surface plasmon resonance of AgNP. The quenching is most likely attributable to nonradiative metallic quenching of AuNP.