Objectives: This paper reports on the results of the study aimed at application of ergosterol as an quantitative indicator of fungal bioaerosol present in the indoor air in occupational environment heavily contaminated with organic dust as well as its comparison with the culturable method. Material and Methods: The study was conducted in the indoor solid waste sorting plant. Using Andersen impactor adapted to 1 plate at the flow rate of 30 l/min, indoor air was sampled in the workers’ breathing zone. Ergosterol was sampled using gelatinous filter (1000 l of air) and then analyzed by means of the spectrophotometric method. Fungi were sampled on malt extract agar (MEA) medium (3 replications: 2 l, 7.5 l, 15 l of air) and analyzed by means of the culturable method. Based on ergosterol analyzes, concentration of fungi was calculated. Results were given as the range assuming min. as 5.1 pg ergosterol/spore and max as 1.7 pg ergosterol/spore. Results: The average concentrations of ergosterol in a working room (arithmetic mean (AM), standard deviation (SD); minimum–maximum (min.–max)) were, respectively: 2.16, 0.72; 0.85–2.92 μg/m³; fungi calculated based on ergosterol – 424.1×10³–1272.4×10³, 140.1×10³– 420.4×10³, 167×10³–1716.5×10³ CFU/m³, and culturable fungi – 13×10³, 9.7×10³, 1.9×10³–34×10³ CFU/m³). It was revealed that concentrations of calculated fungi were even 2 orders of magnitude higher than culturable fungi. Conclusions: The quantitative assessment of moldiness by means of ergosterol measurement seems to be a reliable indicator for environments heavily contaminated with organic dust, where viable and non-viable fungi are present in high proportions. Based on that result, more restrictive (as compared to a similar assessment carried out by means of the culturable method) hygienic recommendations, especially those related to the use of preventive measures protecting the employees’ respiratory tract, should have been undertaken.