Using a two beam, 300 mW laser Doppler velocimeter, the tangential and axial velocity fields were determined for the water flow in a 102-mm modular hydrocyclone. The body of the equipment could be changed to transform it into a conical or a flat bottom hydrocyclone. During the tests the pressure drop and the diameter of apex and vortex were varied and the axial and the tangential velocities and their turbulence intensity were measured. The results shows that the inlet pressure affects only the magnitude of the velocities, but does not change the flow pattern. The tangential velocity is similar in both types of hydrocyclones while the axial velocity is different. In both hydrocyclones the axial velocity is a function of the radial position but, while it is a linear function of the vertical coordinate in the cylindrical hydrocyclone, this is not the case for the conical vessel.