We present an atmospheric-pressure plasma (APP) treatment technique to improve the electrical performance of solution-processed dielectric films. This technique can successfully reduce leakage current and frequency dependence of solution-processed dielectric films. The APP treatment contributes to the conversion of metal hydroxide to metal oxide, and in the case of a solution-treated AlO x dielectric thin film, it effectively ascribes to the formation of high-quality AlO x dielectric thin films. The capacitance of the untreated AlO x dielectric thin film varies up to 9.9% with frequency change, but the capacitance of the APP treated AlO x dielectric thin film varies within 1.5%. When the solution-processed InO x thin-film transistors (TFTs) were fabricated using these dielectric films, the field-effect mobility of TFTs with the APP-treated AlO x dielectric film was increased significantly from 9.77 to 26.79 cm2 V-1 s-1 in comparison to that of TFTs with the untreated AlO x dielectric film. We also have confirmed that these results are similar to the properties of the sample prepared at high annealing temperature including electrical performance, conduction mechanism and chemical structure. The APP treatment technique provides a new opportunity to effectively improve the electrical performance of solution-processed dielectrics in the atmosphere at low temperature.