In this investigation, a centrifugal separator was used to separate grinding chips from grinding fluid. In order to clarify the efficiency of the centrifugal separator, separating experiments were carried out by changing grinding chips (FC, ceramics), its concentration and flow rate of the grinding fluid. They were measured by means of sample bottle way and coulter counter way, and the methods were compared with each other. Furthermore, the minimum size of separated particles by the centrifugal separator was investigated theoretically and experimentally. As the results, the fluctuation of the separating efficiency by sample bottle method was larger than that by coulter counter method. The separating efficiency was increased with the increase of concentration.The influence of flow rate on the separating efficiency was smaller than that of concentration. The minimum size of separated particle was attended to increase with increasing flow rate rather than increasing concentration.It was clarified that the separating efficiency of centrifugal separator was considerably high and enough to use in grinding operation.