The influence of ion implantation of 22 elements on oxidation behavior of intermetallic compound TiAl has been investigated and the mechanisms were discussed. The oxidation resistance was assessed by a cyclic oxidation test at 1200K in a flow of purified oxygen under atmospheric pressure. The possible mechanisms for the improvement are as follows: (1) Formation of a protective Al2O3 scale through β-phase formed in a surface layer, in which Al diffusion is thought fast compared with γ-TiAl; Fe, Nb, Mo, Ta, W. (2) Incorporation of implanted element in TiO2 and a reduction of TiO2 growth rate due to the doping effect; P, Nb, Mo, Ta, W. The implantation of Mg, V or Cr is detrimental due to the enhanced TiO2 growth by this mechanism. (3) Protective Al2O3 layer formation through migration of volatile Al halide; F, Cl. (4) Formation of a complex oxide which promote Al2O3 formation; Zn. (5) Formation of a protective scale of implanted element; Al, Si. On the other hand, the mechanisms for the deterioration can be, (6) lattice defects induced by implantation; Ar, (7) decreased Al concentration in the implanted layer; Se, Ag, and (8) enhanced scale spallation due to a decrease in scale strength; B, N, Zr.