The kinetics of cadmium sorption on to tree fern has been investigated based on the assumption of a pseudo-second order rate law. The batch sorption model has been applied to predict the rate constant of sorption and the equilibrium capacity with the effect of initial cadmium concentration. The experimental results have been analysed by pseudo-Langmuir, pseudo-Freundlich and pseudo-Redlich-Peterson isotherms based on pseudo-second order kinetic expression constant. Both pseudo-Langmuir and pseudo-Redlich-Peterson isotherms were found to represent the measured sorption data well. According to the evaluation using the pseudo-Langmuir equation, the monolayer sorption capacity was obtained to he 16.3 mg/g. In addition, chi(2) analysis was also used to determine the most suitable model. Pseudo-Langmuir and pseudo-Redlich-Peterson were also the best models for the experiment data from chi(2) analysis. (C) 2003 Elsevier Ltd. All rights reserved.