Ag(90.5%)/Sn(9.5%) alloy powders (mass fraction) were prepared by atomization. The oxidation kinetics curves at 600, 700 and 800 °C were obtained using a thermogravimetric analyzer (TGA). The particle size, surface morphology, phase structure and surface composition of AgSn alloy powders were investigated before and after oxidation. Results show that there is negligible difference in particle size before and after oxidation. After oxidation, a rougher surface and slight volume expansion are observed. Moreover, some small holes and cracks appear at the junction of "scales-like section". Based on the controlling diffusion factors, the oxidation phase can be divided into 3 typical stages: exponentially rapid mass gain stage, crossing transition stage and parabolic slow mass gain stage.