How to ensure equal treatment for part-time workers and full-time workers has been a problem faced by drafters of labor laws for a long time. In Taiwan, the number of the part-time workers has been increasing in recent years and therefore this issue has become more important and worth of more discussion. How to ensure equal treatment for part-time workers is an important issue which there was an urgent need to resolve in Japan in recent years. Japan adopted amendments to its labor laws with respect to part-time work in 2007 which prohibited the discrimination against part-time workers and imposed requirements on the employers to treat part-time workers and the full-time workers equally in terms of salary payments, education and training and welfare benefits. Such amendments resulted in great progress in protection for part-time workers. This Article will analyze the development of the Principle of Equal Treatment in Japan and examine the current situation in Taiwan for the purpose of providing a reference for the interpretation of laws and legislation in the future.