Illegal and harmful information on the Internet have been a great concern not only for regulatory authorities, but also all the public institutes, such as public libraries and schools, that provide Internet access service. In particular, for public libraries which play an important role in organizing, opening and providing information resources in the information society, providing Internet access service are indispensible. Therefore, any changes of Internet content regulatory system may have direct effects on services of public libraries. Due to unique characteristics of the Internet, content regulation on the Internet has made a best use of various regulatory methods, ranging from governmental regulation to self-regulation and technical regulatory methods. However, nation by nation, technical regulatory methods on the Internet have been developed in quite different ways. Applying them on public library has been strongly criticised for violating freedom of expression and rights of access to information. This article begins with a theoretical discussion about free speech rights and regulation on Internet. Then it examines filtering software which is one of the most popular technical regulatory methods based on both technical and socio-humanities' prospects and analyses several governments' regulatory approaches to Internet filtering. As a conclusion, issues concerning Internet filtering at public institutes are critically apprised.