The main objective of this study was to develop a simple, energy-efficient photoreactor for operating at room temperature. In this work, the design of a new gas-phase optical fiber photoreactor (OFP) was introduced which operated under various parameters, such as the UV light intensity and the initial concentration for the photocatalytic decomposition of acetone. Experimental results indicated that increasing the UV light intensity or decreasing the initial concentrations of acetone by a UV/TiO2 process would result in improving the decomposition and mineralization efficiencies. The apparent quantum yield of the novel optical fiber reactor is about 2 to 3 times greater than that of the traditional annular reactor.