The effect of surface oxide layer on the activation behavior of TiMn1.25Cr0.25 alloy is discussed through different exposure time to air prior to activation. The activation results imply that activation of TiMn1.25Cr0.25 alloy becomes more difficult with the time of exposure to air prolonging. The auger Electron Spectroscopy (AES) results present that an about 6 nm~10 nm thick oxide layer is formed on the surface of TiMn1.25Cr0.25 alloy, which is a important factor of effect the activation behavior of this alloy. The scanning electron microcopy (SEM) result show that the activation process of TiMn1.25Cr0.25 alloy is closely related with alloy grain fragmentation.