An oxidized mesoporous carbon material, modified with tetraethylenepentamine, has been developed as a highly efficient adsorbent for hexavalent chromium. Influence of parameters such as adsorbent dose (0.1–0.8 g L−1) solution pH (1–9), contact time, and initial concentration (100–1,000 mg L−1) on adsorption capacity has been investigated and optimized. The sorption equilibrium was reached within 60 min. The structural order and textural properties of the synthesized material were studied by X-ray diffraction, scanning electron microscopy, Fourier transform infrared, and nitrogen adsorption–desorption analysis. The experimental results were analyzed by the Langmuir and Freundlich isotherms. The maximum adsorption capacity of 510 mg g−1 at an initial concentration of 1,000 mg L−1 is well predicted by the Freundlich isotherm. The kinetic analysis indicated that the adsorption process was successfully fitted with the pseudo-first-order kinetic model. Compared to other adsorbents reported in the literature, the modified nanoporous carbon material prepared in this study is found to be highly efficient adsorbent for the removal of hexavalent chromium from wastewater.