Microgravity experiments are conducted to measure the thermophoretic velocity, and effects of gas species are investigated. Particles adopted are PMMA spheres of 2.91 mu m in mean diameter, and atmospheric gases chosen are pure gases of argon, nitrogen, and carbon dioxide. The temperature gradient is set at 10 K/mm, and the pressure is set at several conditions in the range from 20 kPa to 100 kPa. Terminal velocities of particles suspended in a gas are individually measured during 0.25 s of the microgravity condition, which is achieved by a free-fall. The accuracy of the measurement is attained by accumulating data from repeated trials. Obtained experimental results are compared with theoretical predictions: a notable discrepancy is found for carbon dioxide, while the results for other two gases are consistent with predictions. Some attempts are made to fix the discrepancy: first by modifying constants and second by modifying two empirical coefficients in the theory. (C) 2012 Elsevier Ltd. All rights reserved.