Abstract: A system and method for improving precision of online advertisement targeting. Upon receiving a search request including one or more search terms, a search engine may identify a list of search results and display the search results in a first portion of a result page. The search engine may also obtain a list of advertisements and display the list of advertisements in a second portion of the result page. If a user is interested in a part of the result page, which may be a search result or an advertisement, he may mouse over it or click on the link to open the web page and get more information. A user activity analyzing module may collect information about the user's browsing activities on the result page, analyze the user's interest, and send one or more supplemental search terms to the search engine, so that the search engine may dynamically update the advertisement list with the supplemental search terms.