Metal-free oxidative degradation by persulfate (PS) is an emerging process as green chemistry without any toxic metal leaching to aquatic environments but has never been explored for natural organic matter (NOM) removal to date. In this study, nitrogen-doped reduced graphene oxide (NrGO) was applied as a catalyst first to investigate the degradation behavior of NOM. A parallel system was also examined without PS for non-oxidative interaction. For three tested NOM, the extent of the removal increased with the addition of NrGO, and the removal rates were consistently higher for the systems with versus without PS (by 25-102%). Specific ultraviolet absorbance (SUVA) exhibited declining trends with NrGO for both oxidative and non-oxidative systems. Up to 86.9%, 59.9%, and 60.3% reduction in SUVA values were found for the oxidative removal of Suwannee River natural organic matter, Suwannee River humic acid, and Suwannee River fulvic acid, respectively. The excitation- emission matrix combined with parallel factor analysis (EEM-PARAFAC) decomposed fluorescent NOM into two fulvic-like (C1 and C2) and two humic-like (C3 and C4) components. Results implied that more hydrophobic and more condensed aromatic NOM constituents might be preferably removed by both oxidation and adsorption with the greater removal tendency shown for the humic versus the fulvic-like components. Size exclusion chromatography (SEC) demonstrated that large size molecules were more effectively removed by the oxidative versus the non-oxidative interactions with NrGO. Comparative results revealed that adsorption likely played a critical role in determining the preferential removal tendency of the metal-free oxidation toward heterogeneous NOM structures.