The present research was conducted with middle school students, 1st, 2nd, and 3rd graders to examine variables related to middle school students\' using mobile phones and general tendencies of school adjustment and analyze the relative influence variables related to the use of mobile phones, sex distinction and grades on school adjustment. The mean and standard deviation were calculated in order to examine the general trend of addictive use of mobile phones, and school adjustment. The summary and discussions of the research results are as follows. First, to examine variables related to using mobile phones and school adjustment, the motives of purchasing mobile phones were that most of other friends around them had cell phones, and they were likely to buy mobile phones so as to contact other people. It was found that when purchasing mobile phones, they mainly bought the products they wanted to, and in relation to the question to ask the reasons that they changed mobile phones, most of their responses were that they had never changed mobile phones, and next, they answered that they changed phones because of mechanical trouble. Third, as a result of examining whether groups had any differences in school adjustment dividing the groups using mobile phones additively into top, middle, and bottom groups, they had significant differences in the overall school adjustment, learning attitudes in class and school rules except relationships with teachers and friends.