The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 ℃ in air by thermal-gravity analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM))were used to examine the oxidized films morphology and the structure after oxidation. Secondary ion mass spectrum (SIMS)method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr2O3 film. Laser Raman spectrum was used to examine the tress changes within oxidized films. It was found that lanthanum implantation remarkably reduced the isothermal oxidizing rate of Co-40Cr and improved the anti-cracking and anti-spalling properties of Cr2O3 film. The reasons were that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide, increased the high temperature plasticity of oxidized film. Lanthanum mainly existed in the outer surface of Cr2O3 film in the forms of fine La2O3 and LaCrO3 spinel particles.