Third generation poly(amido)amine (PAMAM) dendron was grown on the surface of styrene divinylbenzene (SDB) by divergent polymerization method. This new chelating resin (PAMAMG3-SDB) has been investigated in liquid-solid extraction of thorium. The effects of analytical parameters such as pH, contact time, concentration of thorium, resin dose and temperature on adsorption were investigated. Kinetic and isotherm studies of the adsorption were also carried out to understand the nature of adsorption of thorium on the chelating resin. Kinetic data followed a pseudo-second-order model and equilibrium data were best fitted with Langmuir model. The maximum adsorption capacity of thorium ions was determined to be 36.2 mg g-1 at 298 K. Thermodynamic parameters such as standard enthalpy, entropy, and free energy of adsorption of thorium on PAMAMG3-SDB were calculated as -10.498 kJ mol-1, 0.0493 kJ mol-1 K-1 and -25.208 kJ mol-1 respectively at 298 K from temperature dependent equilibrium data. © 2013 Akadémiai Kiadó, Budapest, Hungary.