Although the ”administrative act” has been defined by the law, the definition itself is still indefinite. In practice, it happens pretty often that the administrative action can not meet the requirements set by the definition of ”administrative act”. Different views exist regarding the ways to deal with ”formal administrative act”. Moreover, in order to protect people's rights and to promote administrative efficiency, the inactivity of administrative agencies has been construed as the active permission or agreement by administrative agencies under the regulation of certain statutes. The issues involved with ”constructive administrative act” so far are not well-discussed in Taiwan. The goal of this article is to discuss the subjects concerning ”formal administrative act” and ”constructive administrative act” so that the study in the field of ”administrative act” can be more comprehensive.