Abstract: The objective of this study was to investigate the use of organic polymer resin Lewatit VP OC 1163 to remove the pesticides MCPA, 2,4-D, and Metalaxyl. Freundlich and Langmuir isotherm models were applied to experimental equilibrium data obtained from three measurements (SAC254, COD, and KMnO4 Demand) of pesticide adsorption. The adsorption capacities of the pesticides studied followed the order: Metalaxyl>2,4-D>MCPA. S-type isotherms were obtained, which indicates a moderate interaction between adsorbate molecules and adsorbent. A series of column tests were performed to determine the breakthrough curves using organic polymer resin Lewatit VP OC 1163. The good adsorbability of Metalaxyl on Lewatit VP OC 1163 could be confirmed by the column experiments. The ionic characters of MCPA and 2,4-D are responsible for the short breakthrough times in the Lewatit VP OC 1163 column. It has been concluded that lower the pK a value, the greater is the adsorption for the uncharged (neutral) organic polymer resin. The key parameters that can be derived from this overview are thus, in order of relative influence: pK a, solubility, and hydrophobicity. [Copyright &y& Elsevier]