In livestock houses, particulate matter (PM) and airborne microorganism are two of the most relevant air pollutants. Particulate matter may carry microorganisms, the inhalation of which can cause detrimental health effects. The aim of this study was to study the spatial distribution of airborne aerobic mesophilic bacteria in the air of a broiler farm (rearing poultry for meat production), to quantify the concentration of airborne aerobic mesophilic bacteria and PM in the air and to study their evolution in time, as well as to evaluate the relationship between particle size and airborne aerobic mesophilic bacteria, and to correlate the evolution of PM concentrations and aerobic mesophilic bacteria concentrations. For this purpose, the air of two broiler rooms in an experimental broiler farm was sampled weekly using different methods during 42 days. There was a spatial gradient (p < 0.001) in aerobic mesophilic bacteria concentrations between animal height and higher heights, at the beginning of the production cycle (day 3). The concentration of aerobic mesophilic bacteria in the air ranged from 3 to 6.53 log CFU/m3. Between 42% and 96% of aerobic mesophilic bacteria in the air were found in the particle size ranges between 3.3 to more than 7 µ m. The PM concentration in the air was equal to 0.019 mg/m3 for PM2.5 and equal to 0.189 mg/m3 for PM10.The PM and bacteria concentrations followed a similar evolution during the production cycle (correlation coefficient between 0.78 and 0.89), showing a maximum concentration on day 24 and decreasing thereafter, coinciding with an increase in the ventilation rate.