A method of measuring three dimensional velocity components using a single slanted hot wire probe is presented. The method is applicable to a periodically fluctuating flow and of course to a steady flow. In this method, the hot wire output is measured at three yaw angles of the probe and the nonlinear simultaneous equations which give the velocity components are solved by an iteration method. A smoothing technique is used on the velocity components to suppress the scatter of the components and also to avoid a large error in the measurement. A measurement is carried out in the scroll of a centrifugal fan under the condition that a rotating stall of the vaneless diffuser occurs. The applicability of this method is proved from the experiment.