The article describes both syntheses of diamide derivatives of p-tert-butylcalix[4]arene (3a and 3b) and their immobilization onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe3O4 magnetic nanoparticles to obtain calixarene-based magnetic nanoparticles (CB-MNs). All prepared magnetic nanoparticles (CB-MNs) were characterized by a combination of elemental analysis. FTIR, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The studies regarding the removal of uranyl ion from the aqueous solutions have been carried out both in liquid-liquid and in solid-liquid extraction studies. The results show that the prepared magnetic nanoparticles (4a and 4b) are better removing uranyl ion than the precursor calix[4]arene derivatives (3a and 3b). (C) 2011 Elsevier B.V. All rights reserved.