The purpose of this study was to explore the extent to which the two types of popularity (i.e. sociometric and peer-perceived) respectively predict psychosocial adjustment outcomes (i.e. relational aggression and loneliness) of Taiwanese adolescents. Participants were 864 eighth-graders (50% boys and 50% girls; the mean age is 14.01) from 28 classes of two public schools. The study used peer nomination questionnaire to measure “sociometric popularity”, “peer-perceived popularity”, and “relational aggression”, and a self-report scale to measure “loneliness”. The results show that sociometric and peer-perceived popularity are two distinct constructs. Both popularity types negatively correlate with loneliness. Sociometric popularity negatively correlates with relational aggression, while peer-perceived popularity positively correlates with relational aggression. Lower level of sociometric popularity predicts stronger relational aggression for girls than for boys. Interactions between sociometric and peer-perceived popularity were found to be predictive of both relational aggression and loneliness.