A mathematical model was developed for the cadmium removal process in the free water surface (FWS) constructed wetlands using a dynamic software program STELLA. Earlier, laboratory-scale experiments were conducted at the Suranaree University of Technology Campus in Northeastern Thailand to investigate the effect of high cadmium loading on the performance of FWS constructed wetlands under different environmental conditions. The predicted values of cadmium concentrations in effluents as well as in various components of the FWS constructed wetlands system, as simulated by the developed and calibrated model, had a good agreement with the experimental results. Thus, the mathematical model developed in this study could be used to explain the cadmium removal process in the FWS constructed wetlands. Hence, it could also be used to predict the fate of cadmium in the industrial effluents treated in FWS constructed wetlands system. (C) 2008 Elsevier B.V. All rights reserved.