The B19' martensite phase in Ni-44.55wt%Ti shape memory alloys were investigated by means of the X-ray diffraction. Several X-ray patterns were measured at lower and higher temperature of martensitic transformation and a X-ray pattern simulation by RIETAN-2000 added to determine the crystal structure. At higher temperature than that of martensitic transformation all of crystal consisted in B2 structure. However, the crystal structures at lower temperature of -10℃ consisted in not only B19' but also B2. The ratio of both structures might be 1:1 at martensite phase.
