Characterization of modified humic substances based binders for iron ore agglomeration was examined by chemical analysis, optical density, Fourier transform infrared spectrum (FTIR), and thermogravimetry and differential scanning calorimetry (TG–DSC). Chemical analysis displays the proportion of fulvic acid (FA) to humic acid (HA) in the binder is 1:10. Compared with the HA, the FA possesses more functional groups. Meantime, optical density ratio analysis shows that the molecular weight and aromatization degree of the FA are smaller than those of the HA. FTIR spectra further confirm aromatic and aliphatic fractions are associated with various types of oxygen-rich groups including carboxyl and hydroxyl groups. TG–DSC and chemical analysis indicate structural changes of the binder including thermal decomposition, dehydroxylation and/or decarboxylation are caused during heating. The structural characterization of the binder ensures its good performance in the field of iron ore agglomeration.