Purpose: To develop a tool to evaluate middle school sex education programs. Method: An evaluation tool was developed in 4 stages: first, preliminary items were developed based on the sex education guidebook for teachers published by the Korean Ministry of Education and Human Resources Development; second, a panel of specialists reduced the number of preliminary items by 3 validity tests on the contents; third, final items were selected from the results of pre-test. Finally, reliability and validity were tested by a sample of 601 middle school students of both genders attending all three grades. Result: The developed evaluation tool contained 31 items on the sexual knowledge and 22 items on the sexual attitude. The results of reliability tests were as follows: Cronbachs alpha for sexual knowledge was .84; and for sexual attitude was .88. Conclusion: This study suggested the developed evaluation tool for sex education programs for middle school students had a high degree of reliability and validity. Therefore, it can be utilized to effectively evaluate Korean middle school sex education programs.