Abstract: In order to investigate the deposition of cigarette smoke aerosol in human respiratory tract, a smoking cycle simulator (SCS) was combined with a differential mobility spectrometer (DMS) for online characterization of the particle size distribution from inhaled and exhaled aerosol. Healthy adult smokers were recruited as volunteers who smoked combustible cigarettes, heated tobacco products and e-cigarettes ad libitum. The particle size distributions were fed into a multiple path particle dosimetry model (MPPD) for modeling the aerosol deposition from 3 types of inhaled tobacco products in the human respiratory tract. The results showed that: 1) The size growth factors of the aerosol during smoking were 1.25-1.40, 1.52-2.03 and 1.44-2.43 for cigarettes, heated tobacco products and e-cigarettes, respectively. 2) The aerosol deposition coefficients in the human respiratory tract were in the order of: cigarettes < heated tobacco products < e-cigarettes. 3) The aerosol deposition coefficients from the three types of tobacco products in different parts of the respiratory tract ranked as oral cavity < trachea and bronchus < lung. 4) The aerosol deposition coefficient in the right lower lung lobe was higher, and the highest deposition coefficient was occurred in the 19th-22th airway generations.