The microstructure of Ag-Sn-La alloy powder after oxidation was investigated by XRD, OM and SEM. The results show that Ag, SnO2 and La2Sn2O7 phases are formed in Ag-Sn-La alloy powder after oxidation. Ag-Sn-La alloy powder has different oxidation kinetic characters, oxidation microstructures and oxidation mechanisms due to the different contents of alloying agent. The starting oxidation temperature of Ag-5.2Sn-3.4La alloy powder is 350 oC and the oxidation velocity is fast. Both element Sn and La are oxidized in situ and strip oxides are formed due to the fast oxidation of element La during the oxidation of Ag-5.2Sn-3.4La alloy powder. The oxidation velocity of Ag-6.87Sn-1.28La alloy powder is slow when the temperature is from room temperature to 300 oC and that is fast when the temperature is above 300 oC. Both element Sn and La are oxidized in situ and the formed oxides are uniformly distributed in the silver matrix. The starting oxidation temperature of Ag-9.26Sn-0.44La alloy powder is 567 oC and the oxidation velocity is slow. Element La is oxidized in situ and element Sn diffuses from the inner to the surface due to the driving of concentration gradient. La oxides are uniformly distributed in the silver matrix and Sn oxides are mainly distributed on the grain boundary after Ag-9.26Sn-0.44La alloy powder oxidation.