For faster spindle speed, especially for super high-speed cutting, a spindle with gas or magnetic bearings is a must. However, most investigations on the dynamic characteristics of a spindle system have been limited to the ball bearing type spindles. This work examines the dynamic characteristics of a rotating spindle system with non-contact bearings. For convenience, a spindle with ball bearings is used to elucidate the difference between ball, gas and magnetic bearing spindle systems. A round Euler-Bernoulli beam is used to approximate the spindle. The Hamilton principle is applied to derive the equation of motion for the spindle system. The bearing type and rotation speed effects on the dynamic response of a rotating spindle system are studied.