IntroductionGiven the observed increased feelings of loneliness and problematic smartphone use among adolescents during the COVID‐19 pandemic, further research was needed to determine whether and how the increased loneliness of adolescents during such major public health crisis events affects the risk of problematic smartphone use among adolescents. This study aimed to examine the relationship between loneliness and problematic smartphone use among Chinese adolescents (aged 10–16 years) during the COVID‐19 pandemic and to investigate the possible mediating role of negative emotions and maladaptive coping.MethodsA total of 672 Chinese adolescents (Mage = 13.05, SD = 1.51, 50.4% boys, 93.8% from rural areas, 22.5% of whom were only children) took part in this cross‐sectional study in April 2022 by completing the Chinese adolescent version of the Loneliness Scale, the Positive and Negative Affect Scale (subscale), the Ways of Coping Questionnaire, and the Mobile Phone Addiction Index Scale.ResultsThe serial mediation model revealed that negative emotions and maladaptive coping independently mediated the relationship between adolescents' loneliness and problematic smartphone use. In addition, the mediation effects of “negative emotions‐maladaptive coping” could also mediate the relationship between loneliness and problematic smartphone use.ConclusionsLoneliness may be positively related to problematic smartphone use through negative emotions and maladaptive coping among adolescents during major public health crisis events, such as the COVID‐19 pandemic.