In order to improve the fan characteristics,especially efficiency and noise level of a small axial cooling fan with a large tip clearance,the internal flow measurements with tip leakage vortex were carried out at fan rotor outlet us- ing an I-type hot-wire probe.The probe was set toward two directions,parallel and normal to the meridional plane of test fan,and the two directional velocity components were measured.From the result of fan test it was found that the test fan didn't have the unstable characteristic with a positive gradient on its pressure - flow-rate curve.From the results of velocity measurement it was observed that the tip leakage vortex exited at maximum efficiency flow-rate and large flow-rate conditions.However,at small flow-rate conditions the tip leakage vortex was not observed and it was found that the flow field were enlarged toward radial outwards In order to improve the fan characteristics, especially efficiency and noise level of a small axial cooling fan with a large tip clearance, the internal flow measurements with tip leakage vortex were carried out at fan rotor outlet us- ing an I-type hot-wire probe the probe was set toward two directions, parallel and normal to the meridional plane of test fan, and the two directional velocity components were measured. From the result of fan test it was found that the test fan did not have the unstable characteristic with a positive gradient on its pressure - flow-rate curve. From the results of velocity measurement it was observed that the tip leakage vortex exited at maximum efficiency flow-rate and large flow-rate conditions. However, at small flow-rate conditions the tip leakage vortex was not observed and it was found that the flow field were enlarged toward radial outwards