The hydrophobicity of bituminous coal surface has a significant effect on the separation of coal and mineral matter during flotation process. In this paper, the thermodynamic characterization of the two kinds of liberated fine middling bituminous coal measured by Washburn dynamic method and its influence on flotation have been investigated. Wetting rate and Lipophilic Hydrophilic Ratio (LHR) was calculated by linear regression analysis method according to the wetting process of different density fractions of coal samples wetted by n-hexane, alpha-bromonaphthalene, formamide and water. Washburn equation and Van Oss-Chaudhury-Good theory were used to estimate the surface free energy components of samples. The LHR value of Xiqu (XQ) coal is higher than that of Qianjiaying (QJY) coal, and it decreases with the density level. Density fraction of 1.5-1.6 g.cm(-3) and 1.6-1.8 g.cm(-3) for XQ coal is hydrophobic with similar wetting rate and LHR (7.18 and 6.58), which is consistent with its poor selectivity from the regressive release flotation test. Disperse part of surface free energy reduces slightly with the coal density increase; the base part of coal is increased and all lower than that of the hydrophobic kaolinite (58.27 mN.m(-1)). Furthermore, there is a corresponding relationship between the base part and LHR. Results of elemental analysis and FTIR coincide well with the coal surface property. (C) 2013 Elsevier B.V. All rights reserved.