Abstract: Objective This study was to explore the influence of outdoor environment and indoor personnel activities/behavior on PM2.5 pollution in college student apartments,and to provide scientific reference for protecting physical health of college students.Methods Indoor and outdoor PM2.5 concentrations was measured for 7 days in 9 college student apartments in Daxing District of Beijing;meanwhile,the time-behavior pattern of college students was investigated by the questionnaire.Results The apartment is the most important indoor environment for college students,and they spent 13.30 h per day staying in the apartment,accounting for 55.4%.The range of indoor PM2.5 24 h-average concentration was 39.3-584.1 μg/m3,the over-standard rate is from 66.7% to 85.7%;Outdoor PM2.5 24 h-average concentration was in the range of 76.5-493.2 μg/m3,the over-standard rate is 100%;the average of L/O ratio for indoor and outdoor PM2.5 24 h-average concentration was 0.84 during sampling period.SPSS statistical analysis results showed that indoor PM2.5 concentration was significantly correlated with outdoor PM2.5 concentration,the temperature difference between indoor and outdoor,outdoor relative humidity and wind speed(r =0.792,-0.535,-0.634,-0.547,P<0.01);the influence of indoor personnel activities/behavior on indoor PM2.5 concentration and I/O ratio was also important(P<0.05).Conclusion Influenced by outdoor environment and indoor personnel,indoor PM2.5 pollution is serious in college student apartments.People should take appropriate measures to reduce indoor PM2.5 pollution in the college student apartments.