Background and aims: Individuals with schizophrenia may often experience poor sleep, self-stigma, impaired social functions, and problematic smartphone use. However, the temporal relationships between these factors have not been investigated. The present study used a longitudinal design to examine potential mediating roles of poor sleep and self-stigma in associations between problematic smartphoneuse and impaired social functions among individuals with schizophrenia. Methods: From April 2019 to August 2021, 193 individuals with schizophrenia (mean [SD] age541.34 [9.01] years; 88 [45.6%] males) were recruited and asked to complete three psychometric scales: the Smartphone Application-Based Addiction Scale to assess problematic smartphone use; the Pittsburgh Sleep Quality Index to assess sleep quality; and the Self-Stigma Scale-Short Scale to assess self-stigma. Social functioning was evaluated by a psychiatrist using the Personal and Social Performance Scale. All measures were assessed five times (one baseline and four follow-ups) at threemonth intervals between assessments. Results: General estimating equations found that problematic smartphone use (coefficient5 0.096, SE50.021; P < 0.001), sleep quality (coefficient50.134, SE50.038; P < 0.001), and self-stigma (coefficient50.612, SE50.192; P50.001) were significant statistical predictors for social functioning. Moreover, sleep quality and self-stigma mediated associations between problematic smartphone use and social functioning. Conclusion: Problematic smartphone use appears to impact social functioning longitudinally among individuals with schizophrenia via poor sleep and self-stigma concerns. Interventions aimed at reducing problematic smartphone use, improving sleep, and addressing self-stigma may help improve social functioning among individuals with schizophrenia.  Kulcsszavak: schizophrenia, sleep, smartphone use, social function, stigma, internet addiction, addictive behaviors