Ca ion implantation into equi-atomic Ti-Ni shape memory alloy was carried out to increase the bio-compatibility of this materials by forming a surface barrier which suppress the toxic Ni dissolution from the alloy and the hydrogen absorption into the alloy. Ca ions implanted at the surface layer were also expected to form quasi-hydroxiappatite interacting with bio-structures, during use. With the implantation dose of 3x10(20) ions/m(2), no change in the transformation temperatures or in the shape memory properties was observed. However, a slight change in these temperatures and properties was observed after the immersion of the non-implanted and ion implanted alloys in Hanks solution for several months. These changes are considered to be due to the hydrogen absorption into the alloy during immersion. Higher dose Ca ion implantation seemed to suppress the absorption of hydrogen into the alloy. By the surface analysis using AES, SIMS and XRD, Ca ion concentrated layer whose thickness of several hundred nm was confirmed at the outermost surface of the implanted alloys. The oxide layer which includes Ti and/or Ni was also observed superposing with the Ca ion concentrated layer. XPS analysis of the ion implanted alloys after the immersion in Hanks' solution for 6 months showed the formation of Ca phosphate compounds at the alloy surface.