Abstract: In this study an atmospheric pressure Ar/O2 plasma jet is generated to study the effects of applied voltage and gas flux rate to the behavior of discharge and the metal surface cleaning. The increase in applied voltage leads to increases of the root mean square (rms) current, the input power and the gas temperature. Furthermore, the optical emission spectra show that the emission intensities of metastable argon and atomic oxygen increase with increasing applied voltage. However, the increase in gas flux rate leads to a reduction of the rms current, the input power and the gas temperature. Furthermore, the emission intensities of metastable argon and atomic oxygen decrease when gas flux rate increases. Contact angles are measured to estimate the cleaning performance, and the results show that the increase of applied voltage can improve the cleaning performance. Nevertheless, the increase of gas flux rate cannot improve the cleaning performance. Contact angles are compared for different input powers and gas flux rates to search for a better understanding of the major mechanism for surface cleaning by plasma jets.