In this study, a novel aerosol-based method has been further developed and applied for online investigation of steam gasification kinetics of suspended biomass char particles. When the aerosol method is combined with thermogravimetric analysis, the gasification kinetics were established in a steam (33 vol %)-N-2 atmosphere from 800 to 1300 degrees C for char samples produced from pelletized wood, straw, and miscanthus. The aerosol method includes steps for generating, suspending, and gasifying char particles. The conversion of the char particles was established by measuring the change in particle size distributions and mass concentrations using an aerodynamic particle sizer (APS) spectrometer and a tapered element oscillating microbalance (TEOM), respectively. The reactivity of three char samples could be ranked as wood > miscanthus > straw. The activation energy was 155 kJ mol(-1) for wood char, 199 kJ mol(-1) for miscanthus char, and 222 kJ mol(-1) for straw char. Results interpreted from TEOM and APS measurements indicated that the effective density of char particles initially decreased until a certain level of conversion was reached and then remained constant.