This study examines the influences of parental psychological control on the tendency for smartphone addiction and investigates whether adolescents’ relational aggression mediated the relation of parental psychological control on the tendency for smartphone addiction in adolescents. The sample for this study was 374 students (M 196, F 178) from four middle schools located in Seoul and Gyeonggi-do. Variables were measured with the Psychological Control Scale-Youth Self Report (PCS-YSR), the Peer Conflict Scale (PCS), and the Smartphone Addiction Diagnostic Scale (S-scale). The data were analyzed by means of descriptive statistics analysis, one-way ANOVA, correlation analysis, multiple regression analysis, and the Sobel test. Also, the Baron and Kenny’s model (1986) was used to verify mediating effects. The results are as follow. First, differences in the tendency for smartphone addiction according to gender, the period when participants started using their own smartphone, activities performed most by smartphone, hours of smartphone use per day on weekdays, and hours of smartphone use per day on weekends were significant. Second, parental psychological control, relational aggression, and all subvariables of the tendency for smartphone addiction showed a significant positive correlation. Third, relational aggression turned out to mediate partially between both maternal and paternal psychological control and all subvariables of the tendency for smartphone addiction. The results of this study show that parental psychological control has direct and indirect effects on the tendency for smartphone addiction and describe the mediating effects of relational aggression