This paper presented a prototype axial blood pump with a single-axis controlled magnetic bearing. The magnetic suspension system is realized by using passive magnetic bearings for radial direction balancing, and an electromagnetic actuator to stabilize the axial direction actively. Four methods for measuring axial position of the rotor are presented. Their measurement errors are analyzed with finite element analysis and verified experimentally. The rotor has an inner impeller structure to accommodate fluid flow, and it is driven by a brushless DC motor. A prototype pump was built and tested both in air and in water. The experimental results demonstrated successful pump operations. The rotor can be stably levitated in the air gap.