Abstract: To study the particle size distribution from commercial electric heat-not-burn products, aerosol sample was produced under the Health Canada intensive (HCI) and ISO smoking regimes by a DMS500 fast particulate spectrometer combined with a smoking cycle simulator. The results showed that:1) When the dilution ratio of the aerosol was set as 350:1, the repeatability of the results was better. 2) Under ISO and HCI smoking regimes, the particle size distribution of the aerosol from all the puffs were observed to exhibit an approximate lognormal distribution, ranging from approximately 20 to 200 nm. Under the two puffing regimes, the particle number concentration of the aerosol gradually increased and then became stable with the proceeding puffing. However, the particle number concentration under HCI regime was significantly higher than that under the ISO regime. Under the two regimes, count median diameter (CMD) of the aerosol slightly increased and then became stable, the average CMD for all the puffs was 50.2 and 58.5 nm under the HCI and ISO puffing regimes, respectively. 3) Under the ISO regime, aerosols produced from iQOS^TM or glo^TM heat-not-burn product were different. Particle number concentration from iQOS was significantly higher than that of glo, particle size distribution range from iQOS was narrower than from glo, while CMD of aerosol from iQOS and glo was similar. Under the ISO regime, CMD of aerosol from the heat-not-burn products was slightly bigger than that from an electronic cigarette, while significantly smaller than that from a traditional cigarette. Moreover, the puff-by-puff variations of CMD and particle number concentrations of heat-not-burn products were different from those of traditional cigarettes and electronic cigarettes.