The purpose of this paper is to examine debates on the value conflict between the protection of people’s right, particularly public right of access to government information, and national security in the U.S. as reflected in changes of Freedom of Information Act (FOIA), the foundation of U.S. information access policy. Since 9/11 terrorist attacks, the increased concern regarding national security in the U.S. led to restrictions on people’s right to know and FOIA on the legislative and administrative levels. In this paper, the recent amendments to FOIA and the changes in federal FOIA policies are examined through the investigation of perspectives regarding FOIA implementation, overview of legislation history, and issues on the FOIA amendments since 9/11. The conflict between people’s right to know and national security also have important implications and in South Korea, which has had a sharp confrontation with North Korea for more than 50 years. This was well-illustrated in the serious conflict concerning the restriction on right of access to sensitive government information which emerged during the investigation of 2010 sinking of the ROKS Cheonan. In order to resolve such conflicts in similar terrorism or military incidents in the future,efforts should be made to prepare legal and institutional mechanism. In order to resolve such conflicts in similar terrorism or military incidents in the future, efforts should be made to prepare legal and institutional mechanism including revisions of the Act of Disclosure of Information by Public Agencies, the central freedom of information law in South Korea. The studies of legal and political case on U.S. FOIA in this paper aims to help such efforts.