Phosphorous-modified mesoporous carbon was obtained by thermochemical modification-carbonization of originally synthesized polymeric microspheres with orthophosphoric acid. The obtained material was characterized by physicochemical methods. The adsorption properties of the obtained carbon material towards U(VI) ions were studied and compared to the pristine polymeric microspheres. The highest static adsorption capacity of U(VI) onto studied carbonaceous material (150 mg ‧ g−1) was observed at pH = 1.8 after 2 min contact time. The pseudo-first-order and Langmuir theoretical models were best fitted to the experimental kinetics and equilibrium data. Studied ions present at concentration levels found in natural waters had a negligible effect on U(VI) adsorption onto synthesized carbonaceous material. The adsorption mechanism of U(VI) onto the studied carbon material consisted of surface complexation and interactions with π-π electrons and ion exchange. The synthesized material can be easily regenerated by 1 mol ‧ L-1 NaHCO3 (pH = 12.6). The phosphorous-modified carbon was successfully used both for efficient removal of U(VI) ions from model water samples and for the enrichment of trace levels of U from water samples prior to its determination by the TXRF technique. The LOD for the proposed procedure of U determination by TXRF technique after the enrichment step was 0.011 µg ‧ L-1.