The purpose of this study is to explore the relationships among undergraduates’ sensation seeking motive, Internet psychological need and Internet addiction, as well as to test the mediation effect of Internet psychological need between sensation seeking motive and Internet addiction. The subjects were 411 undergraduates in Taiwan. Structural Equation Modeling was used to analyze the data. The results are as follows: 1. Sensation seeking motive has positive direct effects on Internet psychological need. 2. Internet psychological need has positive direct effects on Internet addiction. 3. Internet psychological need completely mediate the relationships between sensation seeking motive and Internet addiction. Suggestions and implications for education, counseling, and future research are discussed.