The purpose of this study attempts to understand the effect of the principal mentoring program on professional development of the beginning principal in Changhua Educational Bureau. The subjects in the study are some 1-2 years beginning principals and some mentoring principals who provided support, consult, and advices to the beginning principals. The results of the study showed that the principal mentoring program has positive effect for the beginning principals to manage the schools. For example, the principal mentoring program has great assistance on sorting out of tough situation on school administration, and enhanced profession development for the beginning principals and become exceptional principal with highly self-efficacy. There were critical factors to determine the success of the principal mentoring program including the capability of mentoring principals and the match of mentoring principals and the beginning principals. An interesting finding in the study was that the beginning principals looked for more assistance from others besides the official mentoring program.