A new, simple, fast and reliable procedure for the speciation of selenium(IV) and selenium(VI) using Solid-Phase Extraction (SPE) with ammonium pyrrolidine dithiocarbamate/ sodium dodecyl sulfate immobilized on alumina-coated magnetite nanoparticles (APDC/SDS-ACMNPs), followed by electrothermal atomic absorption measurement, is proposed. The method is based on the adsorption of Se(IV) on modied ACMNPs. Total selenium concentration in dierent samples was determined as Se(IV), after reduction of Se(IV) to Se(VI), by heating the samples in a microwave oven with 4.0 mol L1 HCl. Se(VI) concentration was calculated as the dierence between the total selenium content and Se(IV) content. The eect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, and HCl and APDC/SDS concentration ratios as modiers, on the quantitative recovery of Se(IV), was investigated. Under optimal experimental conditions, the preconcentration factor, detection limit, linear range and Relative Standard Deviation (RSD) of Se(IV) were 125 (for 250 mL of sample solution), 0.05 ng mL1, 0.1- 8.0 ng mL1 and 4.1% (for 5.0 ng mL1; n = 7), respectively. This method avoided the time-consuming column-passing process of loading large volume samples in traditional SPE through the rapid isolation of APDC/SDS-ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of selenium in dierent water samples and suitable recoveries were obtained.