By employing a rapid solidification method and atmospheric annealing at 450℃-lhr, we were able to manufacture inexpensively granular CuCo alloy ribbons with thickness of 20㎛ showing giant magnetoresistance (GMR) ratio of more than 5% at a high magnetic field of 0.5T. To verify maximum MR effect, the MR ratio, saturation magnetization, and microstructure change were investigated with Co contents between 5 and 30 at%. It was possible to obtain GMR ratios of 5.2% at l.2T, and 3% at 0.5T, which implies an appropriate MR for industrial purpose at a Co content of 8~14%. MR ratio was reduced rapidly at a Co content below 5% due to superparamagnetic effect and at a Co content above 20% due to agglomeration of Co clusters. Surface oxidation during rapid solidification and atmospheric annealing did not have much affect on MR ratio. Our result implies that our economic CuCo granular alloy ribbons may be appropriate for high magnetic field sensor applications with wide content range of 8~14 at%Co.