In this paper. we develop associate knowledge extraction method for finding and expanding user preference knowledge automatically from web document database. To reflect user interest or preferences, agent explores and extracts relevant information to central term involving the intent of users from the example documents. To do so, we apply association rule exploration data-mining method to the extraction of the relevant objects in the web documents. Also, to give the weighted-value to the extracted and relevant information, we present associate tag block-based weighting method. We applied to bioinformatics above associate knowledge extraction method to find related keywords.