In the 21st century, voices are demanding decentralization of powers as we reevaluate our national structure. The decentralization of government has always been a subject of intense debate in democratic states, since it involves the contentious issues of grassroots political participation and power sharing between levels of government. At the same time, the guarantee of local self-government has become a focus for efforts toward political and administrational reform. Not only in Taiwan but also in Japan, the promotion of decentralization and reforms of local governments, which make local self-government a realization, have become important administrative, political, and legal issues nowadays. Therefore, this paper intends to study and analyze the decentralization and reforms of local governments in Japan and Taiwan from the viewpoints of administration and the Constitution.