This paper deals with the factors degrading magnetic fluid functions. We have two kinds of coagulation of magnetic solid particles in a magnetic fluid. One is formed with a magnetic field and the other without it. The latter coagulation is considered to be caused by the deterioration of surfactants, or the decrease of their thickness around magnetic solid particles and the residual magnetization in them. Such a coagulation has a tendency to make a magnetic fluid inhomogeneous and degrade its function. We have tried to find out the factors affecting on such a coagulation using a centrifuge method and as a result, shearing force of fluid flow, aging of a magnetic fluid and residual magnetization of soild particles were recognized as to be such factors.