A thiol-functionalized hierarchical zeolite nanocomposite was synthesized and investigated with a view to remove mercury from aqueous solutions. The hierarchical zeolite was prepared by the use of a beta zeolite and of cetyltrimethylammoniumbromide (CTAB). The ligand, 3-mercaptopropyltrimethoxysilane containing thiol (–SH) groups, was then immobilized on the surface of the hierarchical zeolite through grafting with surface silanol groups. FTIR, XRD, SEM, TG-DTG, and N₂ adsorption–desorption techniques were used to characterize the nanocomposite before and after functionalization. Adsorption experiments showed that this adsorbent was an excellent one to bind mercury with high selectivity; an adsorption capacity of 8.2mequiv·g⁻¹ of adsorbent was obtained. Furthermore, the adsorbent retained most of its capacity after regeneration with nitric acid and thiourea solutions. The adsorption data was fitted to the Freundlich isotherm.