Three-layer thin films of spin-valve type Co/.u/NixFe100- x at x = 20-80 at.% were prepared by electron-beam sputter deposition. The investigated phase state and magnetoresistive properties were done for as-deposited and annealed to 400, 550, and 700 K films. The measurements of field dependences of magnetoresistance were held at different temperatures. It was demonstrated that phase state, crystal structure, and magnetoresistive properties of Co/.u/NixFe100- x systems strongly dependent on both NixFe100- x composition NixFe100- x and heat treatment conditions.