In treatment of obsessive-compulsive disorder, exposure and response prevention method is one of the most confirmed methods. But exposure and response prevention method have some problems that are high dropout rates and refusal for treatment. To resolve problems, behavioral experimental method was suggested. Behavioral experimental method is one of cognitive therapy techniques. We show the case that combination of exposure and response prevention method and behavioral experimental method is effective for the client. To reduce resistance, behavioral experimental method is more effective than exposure and response prevention method. We teach client that exposure experience is important in behavioral experimental method. In treatment of obsessive-compulsive disorder therapist has to prevent mental compulsions in order to enhance an effect of therapy in addition to prevent overt compulsions. To prevent mental compulsions sharing goal setting and not emphasized cognitive changes are effective.