Abstract: The Co/Cu/Co sandwiches with an amorphous Si buffer layer were prepared by high vacuum electron-beam evaporation. The giant magnetoresistance （GMR） effect in these sandwiches was studied. It was found that an obvious in-plane magnetic anisotropy appeared in the Co/Cu/Co sandwiches with a Si buffer layer more than 0.9nm. A GMR of 5.5% and a high field sensitivity of 0.9%/Oe along the easy axis in Si 1.5nm/Co 5nm/Cu 3nm/Co 5nm sandwich was obtained. The interdiffusion at Si/Co interface was investigated and a cobalt silicide was found. The silicide layer formed at interface was thought to induce the in-plane magnetic anisotropy in the sandwiches, which consequently resulted in the high field sensitivity of GMR.