Aim and Background: Air pollution is considered as one of the major causes of environmental healthproblems. Young children are more susceptible than adults due to age and higher sensitivity health hazards. The aim of study was to investigation indoor/outdoor, regional and seasonal variations of bio-aerosolemission of selected child daycare centers (sites) in Ahvaz city. Materials & Methods: bio-aerosol samplings were performed bimonthly at indoor and outdoor of six sites atdifferent region (industrial, residential, traffic) in a period of 8/12/2015 to 24/5/2016 and three seasons(autumn, winter and spring) in Ahvaz city. Air samplings were conducted by quick take. The flow rate andheight were 28. 3 lit/min and 0. 8-1m above ground level respectively. Collected samples were immediatelytransferred in the cool-box to laboratory for further experiments. Tryptic soy agar (TSA) was used as nutrientmedia for the bacterial growth. After incubation, colonies on each plate were counted and the concentrationswere calculated as colony forming units per cubic meter of air (CFU/m3). Genera identification of culturedairborne bacteria was conducted by examination of gram-stained smears and standard biochemical tests. Itshould be noted that due to the high number of isolates, a number of different colonies were selected basedon the results of microscopic examination and also characteristics such as colony size, colony appearance andpossible pigment from each plate. During sampling, indoor and outdoor temperature and relative humiditywere measured. Results: The results shows that I/O rate of microbial populations at indoor was more than that of the outdoor. The most common bacterial groups found in outdoor and indoor air of the all sites were Gram-positive bacilliand cocci respectively. The highest and lowest concentrations of bacteria were observed in February andNovember respectively. The dominant bacterial genera were Staphylococcus spp. and Bacillus spp. Conclusion: We can conclude that the highest and lowest mean concentrations of bacteria were observed atsites located in high traffic, crowded areas and residential and low traffic region respectively. There is nosignificant relationship between concentration of bacteria and temperature in the sampling sites.