We attempted to add perpendicular magnetic anisotropy (PMA) to half-metallic full-Heusler Co2FeSi (CFS) alloy thin films with potential application in magnetic tunnel junction (MTJ). CFS/MgO stacked structure showed PMA by setting the thickness of CFS below 0.7 nm. It is confirmed PMA is originated from CFS/MgO interfaces. Furthermore, we found that more stable PMA was obtained by introducing oxygen exposure process after the deposition of CFS layer before the preparation of MgO layer. An elongation toward normal direction of CFS lattice is also useful to induce PMA. Contact with Pd(111) crystal plane for CFS upper layer is also effective to induce OMA especially for upper layer. These processes are very useful as methods to modify the structure and chemical state at the interface and effective to form p-MTJ using CFS layers with both half-metallic ferromagnetism and PMA.