Visible-light-sensitive photocatalysts have frequently been used for indoor environmental purification. In order to further expand the applications, improvements in photocatalytic performance are desired. In this study, we have prepared new composite photocatalysts with copper ion loaded tungsten trioxide (Cu/WO3) and copper ion loaded nitrogen-doped titanium dioxide (Cu/N-TiO2) as a function of the composition ratio. Acetaldehyde decomposition activities under visible-light irradiation have been significantly enhanced by the heterojunction photocatalysts at a composition ratio of 1:9 against Cu/WO3 and Cu/N-TiO2. We have also investigated the enhanced mechanisms of the photocatalytic activity using time-resolved visible to mid-infrared (mid-IR) absorption spectroscopy. It has been revealed that there are longer hole lifetimes via electron transfer from the conduction bands of N-TiO(2 )and WO3 to Cu ions, and hole transfer from the valence band of WO3 to that of N-TiO2.