The number of mobile terminals with a Web browser has increased in recent years, and many diverse mobile services using the Internet have evolved. However, there are still limitations such as that it is difficult to change or replace browser functionalities in mobile terminals. This is a factor in service providers being unable to freely provide services. We propose an extensible browser architecture (EBA) to extend the browser functions. The EBA consists of two layers: browser foundation and browser application layer. The browser foundation layer provides the core functions of the browser as Java class libraries, The browser applications, which are written in the Java language and downloadable, utilize modules using the browser class libraries in the browser foundation layer to provide a variety of browser applications. Several applications demonstrate the effectiveness of the EBA.