Despite the benefits of smartphones, many adverse effects have emerged. However, to date, there was no particular approach to treat or prevent smartphone addiction. The aim of this study was to evaluate the therapeutic effectiveness of a home-based daily journal of smartphone use (HDJ-S) in Korean adolescents. Three hundred thirty five middle school students participated in this study. The severity of smartphone addiction was measured using the Korean Smartphone Addiction Proneness Scale. The ability to control smartphone use was evaluated with the Motive Scale for Smartphone Regulation. We used the Parents’ Concerns for Children’s Smartphone Activities Scale to measure parental monitoring and supervision of adolescents’ smartphone activities. The Korean Smartphone Addiction Proneness Scale classified subjects into high risk and non-high risk for smartphone addiction, according to total scores. Forty six participants (14%) were high risk for smartphone addiction. The high risk group performed the HDJ-S for two weeks, and the same scales were subsequently assessed. After performing the HDJ-S, the total scores of the Korean Smartphone Addiction Proneness Scale decreased significantly in the high risk group ( P < 0.001). There was a significant increase in the total scores of the Parents’ Concerns for Children’s Smartphone Activities Scale in the high risk group between baseline and following two weeks of treatment ( P < 0.05). The HDJ-S was effective for adolescents with smartphone addiction and increased the parents’ concerns for their children’s smartphone activities. We suggested that HDJ-S would be considered as a treatment and prevention for smartphone addiction.