Objective: To examine the associations of pet ownership and daily outdoor activity duration with depressive symptoms in middle school students, so as to provide evidence for targeted prevention strategies of depressive symptoms in middle school students. Methods: Using a stratified cluster random sampling method, 83 601 middle and high school students from 103 districts and counties in Inner Mongolia Autonomous Region were selected in 2024. A questionnaire survey was conducted to collect demographic data, household pet ownership, outdoor activity duration, and depressive symptoms of the research subjects. The comparison of reporting rates of depressive symptoms among different groups of middle school students was conducted using a χ 2 test. The association between pet ownership and outdoor activity duration and depressive symptoms among middle school students was evaluated using a Logistic regression model, and stratified analysis was conducted among different genders and regions to control for potential confounding factors and evaluate the stability of the association. Results: The prevalence of depressive symptoms among middleschool students in Inner Mongolia was 17.2%. Significant differences in depressive symptom reporting rates were observed across sex, grade, ethnicity, surveillance site, parental education, menarche/spermarche status, boarding status, smoking and alcohol use, daily breakfast consumption, school bullying, continuous 30 minute headphone use in a noisy environment, and often use the Internet ( χ 2=8.07-2 672.57, all P <0.01). Both pet ownership ( OR =0.78, 95% CI =0.75-0.81) and ≥2 h/d of outdoor activity( OR =0.81, 95% CI =0.78-0.84) were inversely associated with depressive symptoms;compared to the without owning pets and < 2 h of outdoor activity daily group, students who both owned pets and engaged in ≥2 h of outdoor activity daily had an even lower risk ( OR =0.83, 95% CI =0.78-0.87)(all P <0.05). Conclusion Pet ownership and increased daily outdoor activity duration may help mitigate depressive symptoms among middle school students.