In this paper we report the development of a novel actuator for surgical assist manipulator to perform minimally invasive surgery with magnetic resonance imaging (MRI) guidance. The actuator, which is called the spherical ultrasonic motor (SUSM), is constructed of a spherical rotor and three ring-type stators, and has multi-degrees of freedom. In this study, the principle of the SUSM is described. A novel SUSM composed of non-magnetic materials has been constructed, the stator of which was designed using the finite element method. Evaluation of the driving characteristics revealed the SUSM to have good responsiveness and high positioning accuracy. In MRI environment, the noise effects of the SUSM on MRI images were examined. The results demonstrate the feasibility of the surgical assist manipulator using the SUSM.