The adsorption isotherms of nitrate on resin Amberlite IRA 400 at various pH, in the range 2-12, were experimentally determined by batch tests. The experimental data have been analysed using the Langmuir, Freundlich, Redlich-Peterson and Sips isotherms models. In order to determine the best fit isotherm, two error analysis methods were used to evaluate the data: the regression correlation coefficient, and the statistic Chi-square test. In the range of pH tested, the Sips model was found to give the best fit of the adsorption isotherm data. The maximum adsorption capacity can be deduced from the obtained correlation coefficients and was found to decrease for increasing pH. (C) 2008 Elsevier B.V. All rights reserved.