Objective: To investigate loneliness and associated factors among adolescents with mixed anxiety and depressive disorder(MADD), and to provide reference for drawing up effective and targeted interventions. Methods: Using convenience sampling method, 265 adolescents with MADD in Daqing Third Hospital were selected from September 2020 to June 2021. General information questionnaire, Pittsburgh sleep quality index(PSQI), Resilience Scale for Chinese Adolescents(RSCA), Child and Adolescent Peer Relationship Scale and UCLA Loneliness Scale were used to investigate the status and influencing factors of loneliness among adolescents with MADD. Results: The average score of UCLA among 265 adolescents with MADD was (56.49±10.83). The results of univariate analysis showed that age, gender, burden of medical expenses, drinking behavior and parents migrant work had statistically significant differences in the UCLA scores. The results of Pearson correlation analysis showed that loneliness in MADD adolescents was negatively correlated with psychological resilience( F/t=57.65, -60.62, 21.92, 8.52, 16.22, P <0.01), and positively correlated with sleep quality and interpersonal distress( F/t=-0.69, 0.76, 0.50, P <0.01). The results of multiple stepwise regression analysis showed that phase of study, sex, burden of medical expenses, interpersonal distress, sleep quality and resilience were the influencing factors of loneliness among adolescents with MADD( B=0.11, 0.13, 0.09, 0.46, 0.10,-0.24, P <0.01). Conclusion Adolescents with MADD have moderate loneliness, which needs to be improved. Nursing staff should pay attention to the negative emotional experience such as loneliness among adolescents with MADD, and reduce their loneliness by improving sleep quality and resilience, reducing interpersonal distress.