This study investigated uncertainty encountered in description of biosorption data by preset-order kinetic equations. It was shown that for a given set of biosorption data, the kinetic equations with the preset-order of first to fourth can all provide equally good fittings to the experimental data, indicated by comparable values of correlation coefficients (R). In the sense of chemistry, the reaction order of a biosorption process must be experimentally determined rather than preset to a fixed value. In this case, a generalized kinetic equation was proposed without any constrain on the reaction order. In order to statistically evaluate the curve fittings of biosorption data by various kinetic equations, a concept of the relative goodness of curve fitting was developed. Compared to all the preset-order kinetic equations studied, the generalized equation can offer the best prediction for experimental data obtained in various biosorption experiments. (c) 2007 Elsevier Ltd. All rights reserved.