In this investigation, we discussed the flotation behavior of oxidized coal treated by different pre-wetting times. The pre-wetting time is 1 min, 2 min, 3 min, 4 min and 5 min, respectively. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and contact angle measurements were used to indicate the surface properties of oxidized coal. XPS results show that the hydrophobicity of oxidized coal is very low and the oxidized coal should be pre-wetted quickly as there are many hydrophilic functional groups and few hydrophobic functional groups on the oxidized coal surface. In addition, there are also many cracks and holes on the oxidized coal surface from SEM pictures. The cracks and holes should be covered or filled up with water during pre-wetting process. Contact angle measurement results show that the contact angle between the water drop and oxidized coal surface decreases rapidly with the increase of measurement time. Both of the combustible matter recovery and concentrate ash content decrease with the increase of pre-wetting time. (C) 2013 Elsevier B.V. All rights reserved.