Airborne particles have become an important factor affecting the preservation of cultural heritage objects. Monitoring the concentration of particles in the environment of cultural relics, with a view toward preventing damage to these relics has become an important research subject. Up to now there has been little research on this subject in China. A suspended airborne particle counter was used to continuously monitor sizefractionated particulate matter (PM) mass in different display halls of a closed museum, and their concentrations in response to visitors is discussed in this paper. The results indicate that over 95% of the particles are PM0.5 (particle diameter＜0.5μm ) and nearly 80% are PM0.3 (particle diameter＜0.3μm). The impact of visitors on PM number concentration depends on the particle size. The concentration of PM1.0 particles changed little during the entire day, while those particles with PM＜1.0μm showed two peaks:during the morning opening time and during the nighttime cleaning time. The concentration of PM during the holidays was found to be significantly higher than on working days. The studies suggest that in the interest of preserving cultural heritage objects, ambient air particulate pollution monitoring should focus on fine particles.