Purpose: This study was conducted to understand the degree of Internet addiction, Internet expectation and self-efficacy and we also wanted to elucidate the factors influencing this addiction among the high school students in Korea. Method: A total of 348 high school students in the Gyeoung-gi, Daegu and Gyeoung-buk area were surveyed in this study. Data collection was conducted through the use of questionnaires. Results: Internet addiction among high school students in Korea was relatively low. In the overall ratio distribution, however, the students who were classified as either addicted or at risk of addiction accounted were a high percentage of the subjects, 31%. A positive or negative relationship was found between internet addiction and the research variables. Multiple regression analysis revealed that the most powerful predictor of Internet addiction was Internet expectations. Conclusion: Using the above results, it would be necessary to develop an Internet addiction prevention program for adolescents. There should be a qualitative study in the future for an in-depth understanding of internet addiction of adolescents.