Abstract: The principle of GMR sensors for applications in magnetic biosensor was analyzed.Ni₆₅Fe₁₅Co₂0/Cu multilayers were prepared by DC magnetron sputtering.Dependences of GMR on the thicknesses of buffer layer（NiFeCo）,spacer layer（Cu）,and ferromagnetic layer（NiFeCo） were studied,respectively.The maximum GMR of 8.8% was obtained for the as-deposited sample: buffer layer 5nm,spacer layer Cu 2.4nm,ferromagnetic layer NiFeCo 1.6nm,and the saturation field and the hysteresis of the sample were small,which means that the multilayer can meet the requirements of biosensor application.The GMR sensor based on the optimized multilayers was fabricated.Elementary tests were done and in conclusion that the devices can detect magnetic microbeads.