Objectives: This study is to investigate the sexual behaviors among smartphone users of middle school male students. Methods: Data was collected on all students in one middle school of seoul city using a structured questionnaire that is consisted of the detailed fifty-one questions for the five variables, the general characteristics, the features of smartphone obscenity use, sexual knowledge, sexual attitudes and sexual behaviors from Sep. 24 to Oct. 25 in 2015. The responded 480 questionnaires were analyzed by using the SPSS(Statistical Package for the Social Science) WIN 21.0 Program. Results: The results from this study showed that the variables which affected sexual behaviors were school record(high), watching frequency(2-8 times/month, more than 9 times/month), watching reason(solving sexual desire), sexual attitudes, of which sexual attitude was a most influential variable. Therefore, to establish healthy sexual behaviors, it is required to raise correct sexual attitudes. and means that school sex education should make a way of establishing correct sexual attitudes. Conclusions: Professional and systematical sexual education is needed to increase responsible sexual attitude on sexual behaviors.