Nanosize Au-TiO2 is becoming popular to photocatalytic application in visible light. A new fabrication process of photocatalyst is introduced for the purpose of its potential utilization under sunlight. A mixture of photocatalyst and polycarbonate (PC) was cast on a glass substrate to form a film. The photocatalytic experiment was performed in the UV region and visible region separately with powdery samples first, followed by composite films. When powdery Au-TiO2 was applied to decompose of acetaldehyde, activity inferior to Degussa P-25 was observed in UV light, but superior activity was observed in visible light. In the case of Au-TiO2 in PC composite film, evidence of acetaldehyde decomposition was observed, unlike the case of P-25 in PC composite, which showed negligible traces of acetaldehyde decomposition.