In this paper, we propose a Web based agent system called MiSpider, which provides intelligent web services on web browsers. MiSpider enables users to use agents on existing browsers. Users can use MiSpider all over the world only to access the Internet. MiSpider Agent has persistency, and agents condition doesn't change if users change a browsing page. Moreover, agents have a message passing skill to communicate among the agents. Categories and Subject Descriptors H.4.3 [Communication Applications]: Information browsers; H.5.3 [Group and Organization Interfaces]: Web-based interaction; I.2.11 [Distributed Artificial Intelligence]: Intelligent Agent General Terms Design Keywords Browsing Support, Multiagent System, and Information System