One key feature of asphalt aging is the conversion of light components into heavier ones. This study investigates the chemical structural changes of asphalt fractions during aging, with a focus on resins-converted asphaltenes (RCAs), aiming to clarify the conversion mechanism and address controversies over molecular transitions. SARA fractions were aged individually, and RCAs were precisely extracted through secondary separation. Elemental analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance (¹H NMR) were used for structural characterization. The results revealed that the introduction of oxygen-containing groups is the dominant aging pathway, outweighing aromatization and condensation reactions. These polar groups disrupted the π–π interactions of aromatic sheets and reduced the proportion of aromatic hydrogen, but enhanced the degree of aromatic sheet aggregation. The chemical structure of RCAs exhibited significant deviations from asphaltenes and resins, characterized by higher oxygen content and aromatic hydrogen levels, along with smaller aromatic sheet dimensions. Therefore, RCAs cannot be equated structurally with traditional asphaltenes enriched in polycyclic aromatic hydrocarbons. Molecular dynamics (MD) simulations confirmed that the increased polarity of aged resins intensified intermolecular aggregation, thereby reducing solubility in n-heptane. Such aggregation is the main driver of resin-to-asphaltene conversion. This study deepens the understanding of fraction transformations during asphalt aging and provides guidance for accurate modeling and effective rejuvenation strategies.