Abstract: Surface roughness directly affects the mineral surface and water action and plays an important role in the flotation of minerals. There are many studies on the relationship between mineral surface roughness and wettability, but the results are not uniform. In this study, a series of coal flakes with different surface roughness were prepared using sandpaper of different grit sizes and their surface properties were characterised using, for example, contact angle and interaction force measurements. The effect of roughness on the surface wettability of the coals was analysed with the aid of the Wenzel wettability model. The contact angle results show that the contact angle decreases with increasing surface roughness of the coal sample, indicating an increase in hydrophilicity of the coal surface, which may be due to the surface microstructure making it easier for water molecules to enter the surface defects. Spreading and residual force measurements showed that the spreading and residual force of water droplets on the coal surface increased as the roughness increased. As the roughness increased from 0.32 μm to 2.38 μm, the droplet spreading force increased from 159.00 μN to 209.60 μN and the residual force of the droplet increased from 20.74 μN to 23.64 μN. The contact angle and force measurements were consistent, meaning that increasing roughness increased the hydrophilicity of the coal surface and had a detrimental effect on flotation separation.