Nowadays, there is a boom in online purchasing, especially by adolescents. In fact, scholars and marketers alike have long noticed the emergence of adolescent consumers and their consumption behaviors. This research aims at exploring the effect of adolescent decision-making styles on online purchasing behavior, with peer influence as a moderating variable. An online questionnaire survey was conducted on 2,419 adolescents and further verified by regression analysis and analysis of covariance. Adolescents with planned purchase behaviors can be considered as rational consumers, in that they do not care about fashion, or recreational, hedonistic shopping consciousness, but rather focus on brand, price value, and high quality. Indeed, adolescent purchase decision making can be strengthened by peer influence.