There is much interest in co-firing biomass with coal in power plants. Torrefaction is a mild thermal pretreatment (T < 300°C) that improves the milling and storage properties of biomass, making it more like coal, and thus more compatible with existing power plant equipment. We use non-isothermal thermogravimetric analysis to investigate the differences in oxidative reactivities between chars prepared from torrefied and raw willow. Both high- and low-heating-rate chars are investigated. High-heating-rate chars were prepared in a drop tube furnace at a temperature of 900°C with a residence time of 2 s. Low-heating-rate chars were prepared in a crucible in a tube furnace, with a heating rate of 33°C/min, a maximum temperature of 1000 ?C, and a residence time of 1 hour at the maximum temperature. We find that torrefaction has a minimal impact on char reactivities for the low-heating-rate chars, while for the high-heating-rate case the chars prepared from raw willow are over twice as reactive as those prepared from torrefied willow.