Preparation of single-phased indium-doped copper oxide (CuO:In) thin films with high quality at low temperature is crucial for the commercial application of CuO-based solar cells and light-emitting devices. Herein, direct-current magnetron sputtering assisted with high sputtering power and reactive pressure technique was used to prepare monoclinic CuO:In thin films at room temperature. The influence of sputtering power (P-spu) on the microstructure and the optical and electrical properties of the films were studied. The roles of indium in the CuO:In thin films were also proposed. CuO:In thin films are single-phased and monoclinic in structure. The crystallization and the preferred <- 111 > orientation of the films were enhanced with increased P-spu. The red shift of the film absorption edge was due to the decrease and increase of the lattice strains along crystal axes a and b with P-spu respectively. A conducting transition from p type ton type of the films at 100 W P-spu was closely related to the increased substitution of copper by indium. The p- and n-type conductions of the films were mainly due to the copper vacancies and interstitials oxygen and to the effective substitution of copper by indium in the films, respectively. Increased P-spu increased the free carrier concentration and decreased the mobility of the films. The free carrier concentration reached the maxima of 9.333 x 10(18)/cm(3) at 100 W P-spu, whereas the mobility reached the maxima of 23.38 cm(2)/Vs at 60 W P-spu.