When horses are in stalls, they are exposed to airborne particulate matter (PM) (aerosol), including the airborne particles released from stalls' bedding materials because of horses' activities. The aerosol particles are inhaled by the horses and can be a factor in their health and racing performance. We assessed the potential for inhalation and exposure of horses to airborne PM of four different stall bedding materials (straw, shavings, STREUfex, and Woody Pet). The use of straw resulted in the lowest concentration of airborne PM in all three size fractions (PM2.5 = 8.6 ± 5.9 μg/m3, PM10 = 95.3 ± 100.0 μg/m3, and PM total = 184.7 ± 231.9 μg/m3), whereas the use of Woody Pet resulted in the highest (PM2.5 = 10.5 ± 11.5 μg/m3, PM10 = 204.8 ± 258.8 μg/m3, and PM total = 650.3 ± 1157.8 μg/m3). We found significantly lower (P < .0001) aerosol concentrations for the activity type “sleeping” (PM2.5 = 6.54 ± 2.60 μg/m3, PM10 = 80.29 ± 54.69 μg/m3, and PM total = 165.24 ± 137.02 μg/m3) than for “eating” (PM2.5 = 13.36 ± 9.19 μg/m3, PM10 = 230.64 ± 212.26 μg/m3, and PM total = 615.14 ± 649.89 μg/m3) and walking (PM2.5 = 12.92 ± 11.56 μg/m3, PM10 = 224.09 ± 256.90 μg/m3, and PM total = 651.91 ± 1425.56 μg/m3). The use of shavings, STREUfex, and Woody Pet resulted in a higher concentration of airborne particles compared to straw when bedding was disturbed by the horses' activities. The findings point to the importance of choice of bedding with minimal aerosol-generation potential because different bedding materials demonstrated substantially different levels of generated PM, particularly in response to more intense types of horses' activities. The resuspension of the settled PM by the horses blowing and poking into horizontal surfaces within the stalls is a likely cause of acute aerosol inhalation exposure. In addition to selecting bedding materials with the lowest aerosol-generating potential, we recommend evaluation of interventions such as regular wet cleaning and elimination of horizontal surfaces such as window sills accessible to horses in the design of stalls.