The achievement of the ultra-high-speed rotation is needed for performance improvement of the turbo machinery. The ultra-high-speed rotors, supported by herringbone grooved aerodynamic journal bearings, have a good advantage in miniaturization of these machineries. The objective of this work is to study herringbone grooved aerodynamic journal bearings for support and ultra-high-speed rotor. This paper described about the effects of the grooves, the bearing clearance, the groove depth and bearing-support-methods of the herringbone grooved aerodynamic journal bearings in the ultra-high-speed rotational regions. Two types of bearing test device, rigidly support type and O-ring support type, were developed. The experimental works were conducted by elevating the supply pressure and the flow rate gradually with monitoring the behavior of the rotor in vertical type test devices. As the results of this works, a 6.0 mm diameter and 30.75 mm length rotor has been operated at a rotational speed greater than 509 000 rpm by using the herringbone grooved aerodynamic journal bearing which has the groove depth of 4 gm and is supported by two O-rings.