Ti-xNi(x=48.0, 49.0, 50.6, 51.0) alloys are prepared by arc melting at Ar atmosphere. Electrochemical anodization of Ti-xNi(x=48.0, 49.0, 50.6, 51.0) alloys was carried out in 0.2wt% NH4F + 1 vol% H2O + Ethylene glycol.Crystal structure of Ti-xNi(x=48.0, 49.0, 50.6, 51.0 at.%) alloys were investigated by X-ray diffraction. Crystal structure of Ti-48.0Ni and Ti-49.0Ni alloy were B19' martensite(Monoclinic) and crystal structure of Ti-50.6Ni and 51.0Ni alloy were B2 austenite(Cubic). Length of oxide layers formed on TiNi alloys increase as apply voltage and anodization time increase. Also, length of oxide layers formed on pure Ti increase as apply voltage and anodization time increase. However, the growth rate of oxide layers formed on TiNi alloys were different with pure Ti. The growth rate of oxide layers formed on TiNi alloys decrease when anodization time increase from 20 min to 60 min compared with 5min to 20min.Amount of released Ni ions from anodized TiNi samples was higher than from non-anodized samples. This is because of releasement of Ni ions from amorphous oxide layers which have lager surface area. However, it is much less than limit of tolerance of Ni ions and TiNi alloys are available at biomaterials.