The main purpose of this study is to investigate behaviors of mobile phone use and mobile phone addiction tendency of senior and vocational high school students in Keelung city. The survey is conducted using questionnaires, based on stratified cluster sampling. The subjects are high school students from 8 public high schools in Keelung city, with an effective sample size of 927 students. The conclusion of the research findings is as follows, 1. The most used functions of mobile phones are for entertainment and social networks. 2. There was no significant difference of mobile phone addiction tendency between different grades. 3. Mobile Phone Addiction Tendency: A high school student with a smartphone is more likely to become addicted to his/her mobile phone. 4. Moreover, subjects will have a higher possibility of mobile phone addiction tendency the longer they use their mobile phone each day. 5. High school students in the largest degree of mobile phone addiction is "warning level," accounting for 68.3%. In concluding the above survey, the researcher has derived conclusions and presented advice to educational institutions and for future research as a reference to prevent high school students from mobile phone addiction.