Wood char was prepared from wood pellets under controlled pyrolysis conditions. The gasification kinetics for wood char in 33 vol% steam was established in the temperature range from 800ºC to 1300ºC by the combination of thermogravimetric analysis (TGA) and a novel aerosol-based method. The aerosol method was further developed and demonstrated successfully for generating, transporting and gasifying the suspended char particles (0.5-10 µm) in the steam atmosphere at high temperature up to 1300ºC. A tapered element oscillating microbalance (TEOM) was used to measure the change of mass concentrations of particles in the carrier gas, before and after gasification. The activation energy was 155 kJ·mol-1 for wood char with the pre-exponential factor of 3.56×104. This method can be potentially applied to on-line measure the reactivity of char particles directly in hot gas from the gasifier.