The objective of this study is to decompose gaseous acetone ((CH3)2CO) by a self-prepared nano-sized composite TiO2/In2O3/SnO2 film photocatalyst that was prepared by a multi-target vacuum sputter operating at a vacuum pressure of 3 mtorr. The operating parameters investigated for the sputtering process included oxygen to argon ratio (O2/Ar), sputtering temperature, substrate materials, substrate layers, and sputtering duration. The nano-sized composite TiO2/In2O3/SnO2 film photocatalyst was mainly composed of anatase with a few rutile. The surface roughness of the TiO2/In2O3/SnO2 film photocatalyst in terms of RMS ranged from 2.292 to 7.533 nm, while the thickness of the single- and double-layer film photocatalysts were 473.5 and 506.0 nm, respectively. Gaseous acetone was initially injected into and further degraded in a self-designed batch photocatalytic reactor containing the nano-sized composite TiO2/In2O3/SnO2 film photocatalyst. Experimental results indicated that the highest acetone degradation efficiency of 99.9% was obtained at 50°C and 1 atm with the incident of near-UV illuminated by a fluorescent black light lamp. Under the incidence of blue light (430-500 nm), the reaction rates of acetone decomposition were 2.353x10-5 and 3.478x10-5 μmole/cm2-sec for using single- and double-layer TiO2/In2O3/SnO2 film photocatalysts, respectively.