The kinematical characteristics and thermophoretic deposition of inhalable particles with the diameters of 0-2.5 mu m (hereafter referred to as PM2.5) suspended in turbulent air flow in a rectangular duct with temperature distribution were experimentally studied. Particle dynamics analyzer (PDA) was used for the on-line measurement of particle motion and particle concentration distribution in the cross-sections of the duct. The influences of the parameters such as the ratio of the bulk air temperature to the cold wall temperature and the air flow rate in the duct on the kinematical characteristics and the deposition efficiencies of PM2.5 were investigated. The experimental results show that the deposition efficiencies of PM2.5 mainly depend on the temperature difference between the air and the cold wall, while the air flow rate and the particle concentration almost affect hardly the deposition efficiency. 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 thermophoretic deposition efficiency of PM2.5 is presented. The empirical correlation agrees reasonably well with the experimental data.