The purpose of this study was to examine to what extent Internet addiction among adolescents, the mental health level of group under Internet addiction and what types of protective factors affected their mental health. The results are as following; First, 58.0% of the surveyed students were in early addiction, 3.3% were in severe Internet addiction. Overall, 62.2% were addicted to internet. Second, the addiction level of the adolescents addicted to Internet was higher on boys than girls. Third, the adolescents addicted to internet had experienced more obsessive-compulsive, hostility, paranoid ideation and psychoticism than general internet users. Fourth, it was found that the higher level of Internet addiction were more likely to be increased psychiatric symptoms, and the higher level of self-control, conjugal relationship of their parents and friend\'s support were more likely to be decreased psychiatric symptoms.