Abstract This thesis focuses on the oversight mechanism used by congress to supervise the intelligence department, mainly through examining the historical development of the oversight mechanism that the U.S. Congress uses over the Central Intelligence Agency, CIA, as well as evaluating the mechanism¡¦s successes and failures, in order to find a suitable direction for establishing an oversight mechanism for our country¡¦s Legislative Yuan over the National Security Agency, NSA. First of all, the inceptive backgrounds and historical developments of the CIA and the NSA are introduced. After establishing an understanding of the special backgrounds and developments of the two agencies, the writer, using the Institutional Process Theory, analyzes and discusses how the U.S. Congress¡¦ oversight mechanism over the CIA has progressed, thereby determining the key to the successes and failures of the U.S. Congress¡¦ intelligence oversight mechanism. Having analyzed the intelligence oversight mechanism of the U.S. Congress, the writer brings up suggestions as to how our country¡¦s Legislative Yuan can develop an oversight mechanism over the NSA in the future. Lastly, from these discussions, the writer addresses the contributions, propositions, and limitations of this research and hopes that these research and discussions can assist the Legislative Yuan in institutionalizing a comprehensive intelligence oversight mechanism over the NSA.