<p>Indoor campus bioaerosols directly impact the health of students and faculty. Although the COVID-19 pandemic may have altered bioaerosol characteristics in university hospitals, related research remains limited. This study investigated the concentrations, size distributions, microbial compositions and health risks across bioaerosols from four typical sites (NGM: the north gym, SHM: school hospital, CR: classroom, L: library) in 2019 (Pre-COVID). Additionally, we tracked changes in bioaerosol characteristics in the SHM for three years (Pre-COVID: 2019, During-COVID: 2020, Post-COVID: 2021). In Pre-COVID, the bioaerosol concentrations of four sites were as follows: SHM (51 ± 39 CFU/m³) &gt; L (49 ± 20 CFU/m³) &gt; CR (28 ± 18 CFU/m³) &gt; NGM (27 ± 27 CFU/m³). The major bacterial genera identified in four sites were <i>Pseudomonas</i>, <i>Sphingomonas</i>, and <i>Sediminibacterium</i>. Monitoring of the SHM revealed that bioaerosol concentrations increased to 100 ± 66 CFU/m³ in During-COVID and decreased to 69 ± 49 CFU/m³ in Post-COVID, with highest pathogenic risk observed in Post-COVID. In During-COVID, <i>Brevundimonas</i>, <i>Acinetobacter</i>, and <i>Enterococcus</i> were major bacterial genera. Only <i>Enterobacteriaceae</i> and <i>Pantoea</i>, which were not detected in the previous two years were present in Post-COVID. The proportion of fine particle (size &lt; 2.5 μm) was increased every year, from 24.67% to 58.83%, increasing the risk of inhaling potential pathogens. This study elucidated the characteristic differences of bioaerosols in indoor campus environments and highlighted the changes of bioaerosols at SHM after the COVID-19 pandemic, providing important insights for mitigating the inhalation risks of potential pathogenic bacteria and strengthening public health strategies in university settings.</p> Graphical Abstract <p></p>