The composition of particulate matter (PM) emitted from animal feeding operations (AFOs) is complex, and those particulates have negative impact on the health of people and animal in and near the AFOs. To better understand the degree of pollution caused by those PMs, it is necessary to conduct real-time measurement, such as particle sizes and concentrations and so on. The main aim of this study is to evaluate the possibility and effectiveness of the aerodynamic particle sizer (APS) on measuring PM emitted from AFOs. An APS was firstly employed to measure the size distribution of the glass sphere powder and vegetable oil with different attributes in the laboratory. The measurement results were compared with those simultaneously measured by micro-orifice uniform deposit impactor (MOUDI). Then particulate matter emitted from a cattle feedlot was measured by APS at real-time. The result showed that APS performed well when using it to measure two types of glass sphere powder and vegetable oil in the laboratory. According to linear regression analysis, there was correlation between the cumulative mass concentrations of glass sphere powder obtained by APS and MOUDI, as well as the vegetable oil. Both of the values of determination coefficient R2 were greater than 0.9. APS also performed well when using it to measure the particulate emitted from the cattle feedlot since it well recorded the pollution scenarios and reflected the variation of the air pollutant. APS provided values of geometric mean diameter, number concentration and mass concentration, which can be used to evaluate pollution level of particulates emitted from animal feeding operation from different aspects.