In this work, we report the results of an effort to prepare high-quality indium tin oxide (ITO) thin films at a low temperature for flexible organic light-emitting devices (OLED). The ITO films were deposited on 50 μm thin glass sheets (Schott D263 borosilicate glass) using an argon–hydrogen mixture by radio frequency magnetron sputtering. The results show that the conduction mechanism of the films is mainly governed by the scattering of the electrons due to an increased oxygen vacancy and associated ionized impurity scattering centers in the films. At the optimal deposition condition, the ITO thin films with a root-mean-square roughness of 1.13 nm over an area of 300 nm×300 nm, an optical transmission of over 86% in the visible spectrum, and a resistivity of 4.66×10−4 Ωcm were achieved. The films were used to fabricate phenyl alkoxyphenyl PPV copolymer-based OLED. A maximum luminance of 4.8×104 cd m−2 and an efficiency of 5.8 cd A−1 at an operating voltage of 7.5 V for the flexible OLEDs were obtained. The electroluminescence performance of the flexible devices is comparable to the identical devices made using the commercial ITO-coated rigid glass substrates.