The purpose of the current study was to investigate the causal relationship between university students’ aggression and college life adjustment and to test whether smartphone addiction had a mediating effect between the two variables. A sample of 368 students from 5 universities in G Metropolitan City were included in the analysis and structural equation modeling (SEM) was employed to test the hypotheses. The major results were as follows. First, university students’ aggression had a significant positive effect on smartphone addiction. Second, the effect of aggression on college life adjustment was not significant. Third, university students’ smartphone addiction had a significant negative effect on college life adjustment. Fourth, university students’ aggression had a significant effect on college life adjustment through smartphone addiction. Finally, theoretical and practical implications were discussed in terms of enhancing college life adjustment.