The aim of this study was to develop a solid phase extraction (SPE) method for extraction of eleven organophosphorus pesticides (OPPs) from water samples before gas chromatography-mass spectrometry (GC-MS) analysis. The poly(divinylbenzene-N-methacryloyl-L-tryptophan methyl ester) [PDMAT] microbeads synthesized via suspension polymerization of N-methacryloyl-L-tryptophan methyl ester and divinylbenzene (DVB) were used as an adsorbent for SPE of dichlorvos, diazinon, disulfoton, parathion-methyl, malathion, fenthion, chlorpyrifos, bromophos-methyl, chlorfenvinphos, bromophos-ethyl and ethion. A central composite design (CCD), combined with Derringer's desirability function (DF) approach was used for evaluation and optimization of various parameters affecting the extraction efficiency, such as adsorbent amount (g), pH and elution rate of the solvent. The mean relative recoveries for OPPs from the water matrices ranged from 69 to 139% with intra-day RSD of 0.58-8.17% and inter-day relative standard deviation (RSD) of 0.60-4.94%. The PDMAT-SPE method had a good linearity at 1-50 mu g L-1 (R-2 >= 0.987) concentration range and a limit of detection (LOD) in the range of 0.002 - 0.118 mu g L-1, with the exception of diazinon (0.597 mu g L-1). The developed SPE method demonstrated that it could be applied for the determination of OPPs in water samples.