Herein, we investigate the relationship between fuel surface properties and inner resistances of direct carbon fuel cells (DCFCs) by subjecting raw coal to a liquid-phase chemical treatment and correlating its surface property changes (e.g., degree of oxidation, surface area, and ash composition) with those of electrochemical resistances. Fuel surface characteristics are analyzed by thermogravimetry, gas adsorption, and X-ray photoelectron spectroscopy, with correlations established using the Pearson correlation analysis. The obtained results show that the surface Si content is strongly correlated with electrolyte resistance due to influencing the concentration of carbonate ions. Moreover, charge transfer resistance is strongly negatively correlated with the surface oxygen content, since oxygenated functional groups (e.g., carbonyl and quinone moieties) enhance the oxidation of solid carbon by increasing its reactivity and wettability.