The aim of the research was to determine the microbiological quality of atmospheric air in the Tuchów Sewage Treatment Plant, based on the presence of mesophilic bacteria, α- and β-hemolytic bacteria, actinomycetes and fungi. Bioaerosol measurements were made at four points (raw sewage inlet, aeration chamber, puriﬁ ed sewage outlet and 150 m from the treatment plant, at the background point) in the period from January to December 2018. Bioaerosol samples were collected using Andersen’s 6-stage cascade impactor. The tested atmospheric air was characterized by a qualitatively and quantitatively diverse microﬂ ora. The highest amounts of all the studied groups of microorganisms were found at the raw sewage inlet, and in the case of actinomycetes, also twice in the place of biological puriﬁcation. However, there were analyzes in which a higher concentration of microorganisms was observed outside the treatment plant at the control point constituting the background. This applies to bacteria and fungi. The largest source of emission of microorganisms to the atmosphere was the mechanical part of the sewage treatment plant (raw sewage inlet). The tested treatment plant may therefore contribute to the deterioration of the quality of the atmospheric air.