The aim of the study was a mycological assessment of bioaerosol forming during conservative dental treatment, taking into account concentration and type of fungal microflora, and evaluation of the influence of DUWL disinfecting protocol on the fungal contamination of the bioaerosol. The research was conducted on 25 operative sites located in public dental clinics. The air contained in the space between a patient and a dentist during conservative dental treatment with the use of a high-speed handpiece was examined. Air samples were taken using the portable RCS PLUS Air Sampler (BIOTEST AG, Dreieich, Germany) and ready-to-use agar YM Strips for yeast and mould fungi culture. The volume of the sampled air was 100 litres. Before disinfection, the concentration of fungi in the collected air samples at individual operative sites ranged from 4 × 101 cfu/m3 to 34 × 101 cfu/m3. The most common species was Penicillium herquei (62.17% of the total count), followed by other fungi: Alternaria alternata - 12.68%, Penicillium roseopurpureum - 9.41%, Rhizopus nigricans - 5.93%, Aspergillus terreus - 3.89%, Geotrichum candidum - 2.25%, Aspergillus glaucus group - 2.04%, Cladosporium cladosporoides - 1.23% and Penicillium diversum - 0.41%. The concentration of Penicillium herquei at individual operative sites ranged from 0 to 34 × 101 cfu/m3, mean 121.6 cfu/m3, Penicillium roseopurpureum - from 0 to 11 × 101 cfu/m3, mean 18.4 cfu/m3 and Alternaria alternata - from 0 to 18 × 101 cfu/m3, mean 24.8 cfu/m3. After disinfection, like before disinfection procedures, the prevailing species of fungi were: Penicillium herquei, Penicillium reseopurpureum and Alternaria alternata, which amounted to 62.6%, 18.28% and 11.36% of the isolated fungi, respectively. The recorded levels of total airborne fungi were lower after DUWL disinfection compared to those before disinfection.