Air pollution is a public health issue that may cause health problems for workers in the construction industry including workers involved in asphalt paving operations. Epidemiological studies have reported an increase loss of lung function among asphalt workers over the asphalt paving season. Therefore, the goal of this study is to quantify and characterize nanoparticle and ultrafine particle exposure to workers during asphalt mixture preparation activities in an asphalt laboratory. Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution, surface area, mass, and particle concentrations during pouring, mixing, and compaction activities. Particles were also characterized using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) to get a better understanding of their particle size and morphology. Based on the results of the study, the highest number of particles was observed during the pouring process. Laboratory measurement showed that more than 70% of particles in asphalt preparation activities were ultrafine particles, which have diameter smaller than 0.1 micrometer. In addition, the size of the particles obtained by SMPS was compared to the particle size based on the TEM analysis. The estimated sizes obtained by TEM analysis in the asphalt workplace study were in agreement with the estimate size obtained by calculations using SMPS.