In this study, the adsorption of cobalt and lead ions from aqueous solutions by expanded perlite (EP) has been investigated. The effects of several parameters such as pH. adsorbent dosage, and contact time on adsorption process have been investigated. The results of experiments showed that adsorption of both metal ions increased by increasing pH values up to 6.5. Adsorption process was initially fast. The adsorption rate decreased then until reached to equilibrium concentration at 150 and 90 min for cobalt and lead ions, respectively. About 46 and 99% of cobalt and lead were adsorbed onto expanded perlite at equilibrium conditions. The Langmuir. Freundlich and Dubinin-Radushkevich (D-R) adsorption models were used to determine the isotherm parameters associated with the adsorption process. Maximum adsorption capacities of cobalt and lead were 1.05 and 6.27 mg/g, respectively. Thermodynamic parameters for both sorption systems were determined at four different temperatures. The negative values of Gibbs free energy change indicated the spontaneous nature of adsorption process. (C) 2010 Elsevier B.V. All rights reserved.