Pathological Internet Use (PIU) and depression are common problems among adolescents. The incidence rate of PIU varies across different studies from 2.4% to 18.2%，and for depression, it varies from 20% to 44%. Many researchers reported that there was a close association between PIU and depression. However, the direction of causality between the two variables is not clear. Most of the existing researches were cross-sectional and did not discuss the bidirectional relationship between PIU and depression. A few longitudinal studies failed to get consistent conclusion. The goal of the present study is to explore the bidirectional relationship between PIU and depression and its moderators such as gender, grade and internet use preference among Chinese adolescents. The longitudinal data of 1174 adolescents of the National Survey of Adolescent Mental Health in China was used, including 557 male students (47.4%) and 617 female students（52.6%）. All the participants completed self-reported questionnaires for PIU and depression for two times. The average age in the first survey is 14.57±1.84. Cross-lagged model revealed that depression significantly predicted the level of PIU and PIU also significantly predicted the level of depression 16 months later. There is no gender (grade or internet use preference) difference in the bidirectional relationship between PIU and depression. Conclusion: The relationship between PIU and depression was bidirectional rather than unidirectional among adolescents.