Background & Objectives: In recent years exposure to bioaerosols has been an important matter of concern causing danger to human health. This study aimed to determine bacterial and fungal pollution in ambient air of Tehran’s Shahrake Ghods waste water treatment and investigate its relations to environmental parameters. Material and Methods: This cross-sectional study was done in Tehran WWTP for 4 months. 440 samples were taken from grit chamber, aeration tank, aerobic digester, 100 meters apart from the last unit of the treatment plant, and management building of treatment plant by a passive method using 9cm plates. Soy agar and dextrose agar were used for sampling of Trypticase and Sabouraud, respectively. Results: Concentrations varied from 62 to 1823 CFU/Plate for bacteria and from 1 to 50 CFU/Plate for fungi. The highest concentration of bacterial pollution was observed in aeration digester with an average of 3303 CFU/Plate and the lowest one related to grit chamber with an average of 586 CFU/Plate. In terms of fungal pollution, respective highest and lowest numbers were quantified in grit chamber with an average of 61 CFU/Plate and aeration system with an average of 41 CFU/Plate. Dominant species for bacterial were Bacillus, Staphylococcus, and Micrococcus and for fungi were Cladosporium, Alternaria and Penicillium. Conclusion: According to the results, operational and processing units of WWTP influence pollution load and dispersion of bioaerosols. Therefore, appropriate environmental health management in WWTP could be one of the important factors reducing dispersion of bioaerosols.