We have been developing the web search engine, “mondou”, using weighted association rules. It is very helpful for search users to provide associative keywords, which are derived by text mining algorithm. Moreover, based on the experimental results of our web search system, we try to implement these mining functions on web-based intelligent database navigation system using the source program files of the commercial text database “OpenText”. Especially, in order to derive appropriate keywords with small computing cost, we carefully focus on how to determine system parameters, such as Minsup and Minconf threshold values.In this paper, we use the techniques of ROC graph to evaluate the performance and characteristics of derived rules. We propose the ROC analytical model of our search system, and evaluate the performance of weighted association rules by ROC convex hull method. Moreover, we also propose a method, which visualizes association rules using ROC graph to provide the relationship between a query and derived association rules. By using the INSPEC database, we try to specify the optimal threshold values to derive effective rules from the typical bibliographic data.