We employed a descriptive survey to determine the effects of excessive social network service (SNS) usage. Measures of SNS addiction, SNS fatigue, anxiety, and school life adjustment were employed with 209 high school students (85.2% female, 14.8% male). SNS addiction increased as students became more dissatisfied with school life, used SNS for a longer period, and had increased access to SNS as compared with their counterparts. SNS addiction was positively correlated with SNS fatigue (r = .24, p < .001) and anxiety (r = .20, p = .003). SNS fatigue and anxiety were positively correlated (r = .30, p < .001), and school adjustment and anxiety were negatively correlated (r = -.25, p < .001). SNS daily use (in both frequency and number of minutes) and anxiety were associated with SNS addiction (adjusted R = 38.4%). It is necessary to develop intervention programs for vulnerable groups and promote early screening for SNS addiction.