In this article, five particle size fractions such as +0.500 mm, 0.500-0.250 mm, 0.250-0.125 mm, 0.125-0.074 mm, and -0.074 mm were used to investigate the synergistic effect of particle heterogeneity and size on the hydrophobicity characterization of low rank coal surfaces using induction time and wetting thermodynamic measurements. The high induction time result of +0.500 mm size fraction with low ash content proved that the physical property, especially particle size, has a significant effect on induction time and wetting thermodynamic measurements. Moreover, LHR value and combustible recovery of 0.250-0.125 mm size fraction were higher than that of 0.125-0.074 mm size fraction, which indicated that the induction time measurement was greatly affected by the chemical property, i.e. heterogeneity. Furthermore, wetting thermodynamic measurements can be used as the supplement of induction time measurements while the ash content of the particle size fractions is close.