The kinematic characteristics and thermophoretic deposition of inhalable particles（PM2.5）suspended in air flow in a vertical 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.Influence of the parameters such as the ratio of the bulk air temperature to the cold wall temperature in the duct on the kinematic characteristics and the deposition efficiencies of PM2.5 was investigated.Experimental results indicate that the particle concentration distribution in the duct，extremely in the area near the walls，is mainly determined by the turbulent diffusion in the flow，but turbulent diffusion is hard to make particles to deposit on the dust walls. Thermophoresis is the key factor to the particle deposition on the cold duct walls.Based on the experimental results，an empirical correlation for the calculation of thermophoretic deposition efficiency of PM2.5 is developed.The empirical correlation agrees reasonably well with the experimental data.