Purpose: This cross-sectional study was done to compare factors influencing smartphone addiction in middle school boys and girls. Methods: Participants were 390 middle school students (boys 198, girls 192) who were living in Seoul. Data were analyzed using SPSS 20.0 program. Results: Factors influencing smartphone addiction for boys were stress, the motivation to use smartphone as a tool of ostentation and fashion, depression, self-control, and teacher control over the use of smartphone. Factors influencing smartphone addiction for girls were stress, the motivation to use smartphone as a tool of ostentation and fashion. Conclusion: The results suggest that it is necessary to consider gender characteristics in order to develop effective management programs for smartphone addiction in middle school students.