In order to understand the influence of spanwise loading distributions of mixed flow impellers on internal flow patterns of a pump, the pressure distributions on the pump casing wall were examined for four impellers. They had identical sectional blade shapes on every development surface, and their inlet and outlet angles were kept constant at the mean surface but were varied at the tip and hub surfaces to give spanwise loading distributions. The results of the pressure measurements were compared with oil flow patterns of the suction surface of the impeller blade, and the relationship between the flow conditions of pump internal flow and the pressure distributions was clarified. Three dimensional calculations by the finite-element method were also carried out.