It is a difficult problem that learner have to need much times and efforts to search informations for problem solving. This is caused that the web based search system used by this time have the searching method of simple keyword matching. The searching method of simple keyword matching search informations by method of whether it is simply matched with keyword. Therefore, Learner have to much times and efforts to search informations, and may lose or be out of his bearing. To solve this problems, We design and implement a ontology based search system. This system is apply to PBL of social studies on middle school students. As a result, This system is more effect than the web based search system used by this time.