As personal computers and Internet have become widely popular, our lives have been changing with the increasing effect of them. The development of Internet gives benefits on our lives in that we could access to information rapidly and accurately. However, Internet has side effect, called “Internet addiction”. Internet addiction is defined as a symptom that Internet users have problems on daily life, social life, mental and physical health, and finance using Internet too much. Especially, adolescents using Internet longer than adult have these problems. Therefore, the purpose of this study is to find out what extent of the Internet addiction is and examine the relationship between the middle school students\' Internet addiction and adaptability of school life and democratic citizenship. In order to analyze their relationship, questionnaires on Internet addiction, adaptability of school life and democratic citizenship are composed. 400 middle school students in the Seoul are randomly sampled. Collected data by the questionnaires are analyzed by various statistical methods such as frequency, χ², t-test, one-way ANOVA, ANCOVA, stepwise multiple regression. According to the results of the survey, First, 44.2% of subjects show the symptoms of Internet addiction. students making bad marks at school and a door-key students show Internet addiction Second, the lower grade, the higher marks at school and the higher standard of living, the more positive and affirmative of adaptability of school life. the lower grade and the higher marks at school, the higher democratic citizenship. Third, significant differences are found in the scores of adaptability of school life between Internet addicted students and non-Internet addicted students. That is, Internet addicted students show lower scores than non-Internet addicted students. Fourth, significant differences are also found in the scores of democratic citizenship between Internet addicted studentsand non-Internet addicted students. That is, Internet addicted students show lower scores than non-Internet addicted students. In conclusions, Internet addicted students don\'t adapt school life and have a low democratic citizenship. Namely Internetaddiction have a negative effect on adaptability of school life and democratic citizenship. In order for Internet to be properly established, it is necessary to develop education program and conduct campaign to change the current Internet culture.