Air pollution is one of the environmental problems, especially in developing countries such as Iran. In addition to the chemical composition of air pollutants, microbial air pollution is also important due to its negative effects on human health. Particles matters (PMs) are considered as an important indicator of ambient air quality. According to the trend of air pollution in Isfahan City and microbial population in this area and its relationship with PMs. The aim of this study, therefore, was to investigate the population increasing relevant diseases, it is important to study the atmospheric of bacteria in PM 2.5 , PM 10 and total suspended particles (TSP) sampled from 4 different stations of Isfahan City (Bakhtiar dasht station located in the north of Isfahan City, Jey terminal station located in the east of Isfahan City, Soffeh terminal station central part of the city), on February (cold season) and July (warm season), 2019. located in the south of Isfahan City and Imam Hossein Square station in the The PM samples were collected using an air sampling pump on culture media and incubator at 37 o C. The PM the number of bacterial colonies was counted after 48 hours’ growth in the concentrations and some morphological characteristics of bacteria were also investigated. Besides, the concentration of PMs and some morphological characteristics of bacteria (such as shape and Gram test) were investigated. The results TSP PM 10 PM 2.5 . The bacterial population at two stations showed that the trend of bacterial colonies number in different particles was in north and east of the region (Bakhtiar dasht and Jey stations) in the warm season was higher than of the cold season, whereas it was reversed in the other two stations at south and center of the city (i.e. Soffeh and Imam Hossein pollution including natural and anthropogenic sources that affected the eastern Square stations), which seems somehow to have been the result of the type of and northern regions in summer. The highest number of bacterial colonies in TSP, PM 10 and PM 2.5 particles was seen at Jey terminal station in warm season which were 357, 299 and 271 CFU / m 3 , respectively. This area is also affected by desert suspended particles in summer. Overall, in both summer and winter sampling periods, the percentage of gram-positive bacteria in all stations was higher than gram-negative bacteria. This study highlights the importance of PMs pollution especially PM 2.5 as the carrier of microbial pollution in the atmosphere which can adversely affect human health. It is also recommended to study the pathogenicity of ambient air bacteria in the study area in future studies.