The information on the Web is increasing explosively, and the Internet/Web has become the information infrastructure of our own time. Web users gather and find information through search engines using keywords related to their interests. However, it is not always the case that users conceive suitable keywords relevant to the problem in question. In this paper, we propose a novel method for query expansion based on the user profile generated from browsing histories of a user. This enables a user the context-sensitive keyword expansion using profiles specific to the user. Here, we assume that a user's web browsing behavior corresponds to the user's intended query. We illustrate the usefulness of our proposed method for query expansion with some examples.