Abstract: To gain a deeper understanding of the relationship between organic matter and the formation of sandstone-hosted uranium deposits, representative low molecular weight organic ligands were selected from the thermal pyrolysis products of humic substances associated with sandstone uranium ores, and density functional theory (DFT) calculations were employed to evaluate the coordination capability of these organic ligands toward U(Ⅵ). On this basis, O-benzyl-L-serine was selected for experimental validation of the DFT results, and the corresponding complexation constants with U(Ⅵ) were measured via the Schubert cation exchange method. The results clearly show that all the organic compounds containing carboxyl (-COOH), carbonyl (-C=O), and amino (-NH₂) groups in the thermal pyrolysis mixture can spontaneously form complexes with U(Ⅵ). The predominant interaction governing complex formation is revealed to be electrostatic attraction, which constitutes the fundamental driving force for the coordination bonding. A detailed examination of the frontier molecular orbitals reveals that the highest occupied molecular orbital (HOMO) of the resulting complexes is predominantly localized on the 2p atomic orbitals of the oxygen atoms belonging to the organic ligands, whereas the lowest unoccupied molecular orbital (LUMO) is mainly composed of the 5f orbitals of the central uranium atom. Moreover, each bond between the uranium atom and the donor atom is characterized as a single bond, and the overall bonding nature exhibits the characteristics of an ionic bond. The calculated bond order strengths follow a clear decreasing order of U-O_COOH＞U-O_C=O＞U-N. When the complexation experiments are conducted at pH values ranging from 3 to 6 and temperatures between 25 and 40 ℃, the coordination behavior of O-benzyl-L-serine with U(Ⅵ) is found to be strongly dependent on both acidity and thermal conditions. Nevertheless, the resulting complexes maintain a high degree of stability over this entire range of pH and temperature, which corroborate the DFT predictions very well. This study demonstrates that low molecular weight organic ligands derived from the active structural moieties of humic substances associated with sandstone-hosted uranium deposits are capable of forming stable complexes with U(Ⅵ), thereby providing both theoretical evidence at the molecular scale for understanding the influence of associated organic matter on the geochemical behavior of uranium, and offering new perspectives for further investigating the role of organic matter in the formation of sandstone-type uranium deposits.