Introduction: Exposure to pollution due to bioaerosols almost is an inescapable feature of urban living throughout the world. Contact with ambient microorganisms with a wide range of harmful effects on health. Air microbes can cause respiratory infections in patients with immune deficiency and are responsible for communicable diseases. The main objective of this study was to measurement of Actinomycets concentration and impact of environmental parameters on concentration of actinomycetes in normal and dusty conditions and in Ahvaz city.

Materials & methods: In this descriptive- cross-sectional study, The air sampling was performed by Air trapping method from the level of respiratory (height 5.1 meters) by the quick take 30 system with a flow rate of 14.3 L/min within 5 and 15 minutes at different stations during the summer, fall and winter in Ahvaz for 9 months (183 samples in total). Sampling was performed at normal conditions in two times per day: morning (9–12) and afternoon (14:00–17:00) and for dusty condition (morning, noon and afternoon). Colonies grown on a nutrient medium (TSA) was counted by using direct method and colony counter and was expressed in terms of colony forming units per cubic meter (CFU m-3). The obtained data was analyzed by SPSS and Excel software.

Findings: The number of colonies of actinomycetes in dusty days was 2.5 times than normal days (1.66 times). Winter was more polluted in the case of actinomycets concentration. There was a significant association between particle concentration with the number of colonies formed in cubic meter of air and there was a negative relationship between actinomycets concentration and ambient temperature, while a positive association was observed between wind speed, PM2.5, PM10 with actinomycets concentration.

Discussion & Conclusion: whatever environment has more population density and traffic, and low vegetation, the concentration of bacteria and actinomycets in environment is high.