A molecular-imprinted polymer nanoparticles (MIP-NP) for the selective preconcentration of 2,4-dichlorophenoxyacetic acid (2,4-D) is described. It was obtained by precipitation polymerization from methacrylic acid (the functional monomer), ethylene glycol dimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile (the initiator) and 2,4-D (the template molecule) in acetonitrile solution. The MIP-NPs were characterized by thermogravimetric analysis, and by scanning electron microscopy. Imprinted 2,4-D molecules were removed from the polymeric structure using acetic acid in methanol (15:85 v/v %) as the eluting solvent. The sorption and desorption process occur within 10 min and 15 min, respectively. The maximum sorbent capacity of the molecular imprinted polymer is 89.2 mg g⁻¹. The relative standard deviation and limit of detection for water samples by introduced selective solid phase extraction were 4.2% and 1.25 μg L⁻¹, and these data for urine samples were 4.7% and 1.80 μg L⁻¹, respectively. The method was applied to the determination of 2,4-D in the urine and different water samples.