A photocatalytic assembly (100) includes a substrate (110) and a photocatalytic unit (120) laminated on the substrate (110). The photocatalytic unit (120) includes a laminated titanium dioxide layer (122) and a metal layer (124). The titanium dioxide layer (122) has a thickness of 10 nm to 100 nm. The metal layer (124) is formed by stacking metal nanoparticles. The metal nanoparticle is made of at least one selected from the group consisting of rhodium, palladium, platinum, gold, silver, and aluminum.