Relations between giant magnetoresistance (GMR) characteristic, magnetic properties and structure were investigated in Cu90Co10 alloy obtained by melt spinning in which GMR was enhanced by appropriate annealing. The structure of the annealed sample is not homogeneous (though the sizes distribution of the majority of Co-particles is not very wide but much larger particles are also present). On the other hand, the GMR characteristics differs from that expected theoretically for identical superparamagnetic particles. It is shown that ther main sources of the observed non-quadratic magnetoresistance dependence on magnetization are differentialted surface to volume ratio of superparamagnetic particles and the ferromagnetic phase contribution to the total magnetization which was calculated applying the new method.