The aim of this project is to investigate the photocatalytic activity of ZnO/TiO2 composite films for the gas-phase oxidation of ethanol. Pure TiO2, pure ZnO, and their composites were formulated using a sol-gel synthesis method, and the resulting powders were cast and dried as thin films in a flat plate ultraviolet light-emitting- diode (UV LED reactor. P25 TiO2 and commercially-available ZnO were also used for comparison. Structural, morphological, and optical characteristics of the materials were characterized. The photocatalytic oxidation of ethanol vapors in air after 24 hours of reactor operation was used to assess the relative photocatalytic activity of the ZnO/TiO2 composite films. Our results show that as ZnO composition in the photocatalytic film increases, the apparent photocatalytic activity decreases, and pure ZnO (both sol-gel and purchased) had the least photocatalytic activity for vapor-phase ethanol oxidation in our test apparatus. ZnO-containing photocatalysts have lower surface areas than those of TiO2-based photocatalysts. For gas-phase photocatalysis, surface area was shown to be a critical feature for photocatalytic activity.