Bare-magnetite nanocrystals with an average size of 10 nm, synthesized using the co-precipitation method, were functionalized with sodium oleate (SO) in aqueous media. The SO-magnetite nanocrystals were then functionalized with meso-dimercaptosuccinic acid (DMSA) through a ligand-exchange process. Ultrasonication of the magnetite promoted the ligand-exchange reaction; suitable functionalization with DMSA was achieved after 1 hour of contact. The actual functionalization of the nanocrystals was verified using Fourier transform infrared and Raman spectroscopy techniques. The adsorption capability of bare-magnetite, SO-magnetite and DMSA-magnetite nanocrystals for arsenate and arsenite aqueous species was assessed at different pHs. The DMSA-magnetite exhibited the maximum uptake capacity of 14.05 mg/g for arsenate species at a pH 6.5, whereas bare magnetite showed the highest uptake capacity of 11.53 mg/g for arsenite species at a pH 7.5. The adsorption isotherms fit the Freundlich model. Scatchard plots for arsenic species sorption suggested that the adsorption process took place via a single-step process.