Objective: To explore the status of PM 2.5 pollution in school classrooms and the student exposure level, and to provide basic data to safeguard the health of students. Methods: This study continuously monitored the PM 2.5 levels of 16 naturally ventilated classrooms in eight primary and secondary schools in Jiamusi for one academic year using an online environmental monitoring instrument. At the same time, outdoor PM 2.5 data was captured for comparative research, and student exposure to PM 2.5 during school hours was evaluated. Results: The average concentration of PM 2.5 in the classroom in the spring and autumn semesters was (26.93±24.7) and (31.85±30.37)μg/m 3, respectively, and the indoor/outdoor ratio ( I/O ) was 0.92 and 0.95, respectively, which indicated a strong correlation between them. The daily average concentration of all classrooms during both semesters was ( 28.93 ±26.85)μg/m 3, which was slightly higher than the average concentration of (27.53±26.53)μg/m 3 during the daytime when students were in school. In addition, the concentration on workdays was higher than that observed on weekends, and this was termed the "weekend effect". The indoor PM 2.5 concentration was lower on higher floors. The comprehensive exposure concentration of students during school was 28.48 μg/m 3 in spring semester and 31.87 μg/m 3 in autumn semester. Conclusion PM 2.5 levels in the classrooms varied according to time, the horizontal space, and the vertical space, and the level of indoor PM 2.5 pollution largely depended on outdoor pollution sources. Differences in PM 2.5 exposure were observed between.