The kinematical characteristics and thermophoretic deposition of inhalable particles with the diametersof 0-2.5μm (hereafter referred to as PM2.5) suspended in turbulent air flow in a rectangular duct with temperaturedistribution were experimentally studied. Particle dynamics analyzer (PDA) was used for the on-hne measurementof particle motion and particle concentration distribution in the cross-sections of the duct. The influences of the pa-rameters such as the ratio of the bulk air temperature to the cold wall temperature and the air flow rate in the ducton the kinematical characteristics and the deposition efficiencies of PM2.5 were investigated. The experimental re-sults show that the deposition efficiencies of PM2.5 mainly depend on the temperature difference between the airand the cold wall, while the air flow rate and the particle concentration almost affect hardly the deposition effi-ciency. The radial force thermophoresis to push PM2.5 to the cold wall is found the key factor for PM2.5 deposition.Based on the experimental results, an empirical modified Romay correlation for the calculation of thermophoreticdeposition efficiency of PM2.5 is presented. The empirical correlation agrees reasonably well with the experimental data.