It is very important to investigate the airborne microorganisms due to the fact that the biodeterioration can be induced by such microorganisms. In this study, the Anderson FA-I air sampler was used for the sampling of airborne microorganisms both in a closed cave (closed to all visitors) and at an outside site (the entrance gate) at the Mogao Grottoes. It was found that the concentration of airborne bacteria in the cave was much higher than the outside, but no significant difference in concentration of fungi was observed between the two sites. There were slight variances of airborne microorganism concentrations according to the season, the highest fungi concentration season outside being during the summer. Inside the case, the bacteria concentration was the highest during winter. The significant positive correlations were made between the outside cave bacteria concentration and air temperature, solar radiation, surface temperature and wind speed, while a negative correlation was seen with air relative humidity. Meanwhile a positive correlation was found between outside cave fungi correlation and the number of visitors. The airborne bacteria mainly distributed on stages 1, 3, and 4, and fungi at stages 2, 3, and 4. The most abundant fungi found in the Dunhuang Mogao Grottos were Cladosporium, and the non-sporing fungi: Penicillium, Alternaria and Aspergillus.