In the present study, the sorption behavior of cesium was investigated in Ain Oussera soil around the Es-Salam reactor facility. This study was conducted using batch method under different physicochemical conditions including contact time, ionic strength, pH, solid/liquid ratio and temperature. The results showed that sorption followed pseudo-second-order kinetics with a good regression coefficients (R-2=0.999). The activation energies were 11.26 and 15.21 kJ mol(-1) which correspond to ion-exchange-type sorption mechanism. The adsorption was favored at low temperature and it was exothermic (Delta H-0 <0, with average value of -1.97 kJ mol(-1)) and spontaneous (Delta G degrees < 0, with average value of -11.97 kJ mol(-1) at 23 degrees C and -13.2 kJ mol(-1) at 60 degrees C). The presence of competing cations such as K+ and Ca2+ ions in groundwater can significantly reduce the Cs adsorption onto soil. Desorption reaction was also investigated using three reagents with different ionic strengths (deionized water, groundwater and 0.1 M KCl solution). The results showed that Cs ions were preferentially distributed onto high affinity sorption sites. (C) 2010 Elsevier B.V. All rights reserved.