Buffer (t $AA$)/ CoFe(35$AA$)/Cu (50$AA$)/Co (35$AA$) sandwiches prepared by dc magnetron sputtering on Corning glass substrates using the $Co_{90}Fe_{10}$ and Co layers with different coercivities. Dependence of magnetoresistance on the type and thickness of buffer layers, and on the thickness of Cu and the magnetic layers in buffer/ CoFe/Cu /Co sandwiches were investigated. Magnetoresistance ratio and saturation field $H_s$ increased as thickness of the buffer layer becomes thicker, then decreased smoothly after a maximum value. An improved filed sensitivity was realized with the $Ni_{81}Fe_{19}$ buffer layer.