The co-gasification behavior of deoiled asphalt (DOA) with coal and biomass were investigated by a thermogravimetric analyzer (TGA). The gasification experiments were conducted under CO2 atmosphere within an isothermal temperature range from 900 to 1100 degrees C. The physical properties of the samples were examined by X-ray diffraction (XRD), scanning electron microscopy energy dispersive spectroscopy (SEM EDS), N-2 and CO2 adsorption and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Compared with coal or biomass, the low surface area, high graphitization degree and the low ash content are the main reasons for the low reactivity of DOA. The co-gasification of coal and DOA does not show synergetic effect, while the combination of biomass and DOA shows higher gasification reactivity than that of being calculated. The synergetic effect is mainly caused by the alkali metals. Further study shows the transfer of the potassium from the surface of biomass to DOA greatly increases the active sites of the DOA, which leads to obvious improvement of the co-gasification reactions. Meanwhile, the gasification experiments of adding coal and biomass ashes to DOA also support the above explanations. (C) 2014 Elsevier Ltd. All rights reserved.