The temperature dependence of Co anisotropy on a nano- Fe Ox layer was studied in the structure of IrMnCo (FM1) Fe Ox Co (FM2). An anisotropy transition of the FM2 was observed from a combination of uniaxial and unidirectional anisotropies at room temperature (RT) to unidirectional anisotropy at temperature below 80 K through field cooling process. Various ferromagnetic (FM) and antiferromagnetic (AFM) components existing in the Fe Ox layer were attributable to the observed anisotropy of FM2. AFM domains with TN higher than room temperature were responsible for the observed uniaxial anisotropy at RT and AFM domains with TN of 80 K were accountable for the anisotropy transition, below which the unidirectional anisotropy became dominant. In addition, the direction of the shifted loop could be determined by the cooling field direction.