Abstarct: In this study a sensitive, selective and simple dispersive solid phase extraction was developed for the preconcentration and determination of Nitrazepam (NTZ), Alprazolam (APZ), Chlordiazepoxide (CZP) and Diazepam (DZP). The method is baxsed on the adsorption of analytes on the iron oxide nano particles modified by polyaniline (Fe3O4/PANI) and subsequently complete washing with acetonitrile as elution solvent. High performance liquid chromatography (HPLC) was used for separation and detection of analytes. The effect of chemical and instrumental variables on the preconcentration and determination of analytes were investigated and optimized. Under the obtained optimum conditions, the peak area (analytical signals) and analytes concentrations have linear behavior over range of 0.05-6.00, 0.01-5.00, 0.03-7.00 and 0.03-6.00 mg L-1 for NTZ, APZ, CZP and DZP respectively