In this study, nanocomposites composed of magnetite nanoparticles (MNPs) coated with polyaniline fabricated by in situ polymerization were prepared for arsenic adsorption. Properties of particular MNPs and their nanocomposites were characterized with scanning electron microscopy, X-ray diffraction spectroscopy, and Fourier transform infrared spectroscopy. The As(III) concentration before and after adsorption on nanocomposites was detected by atomic absorption spectroscopy method and then compared with the results measured by a self-developed potentiostat system with anodic stripping voltammetry method. The polyaniline coating resulted in an improvement for As(III) adsorption ability of magnetite nanoparticles, and among the three compositions of PAni/MNP nanocomposites, the 5 wt% PAni showed the highest capability of As(III) adsorption (or removal) of 50 mg/g. Performing pH investigation, the concentration of remaining As decreased when pH increased from 2 to 5 and reached saturation value at higher pH. Above all, the electronic device can be integrated with As(III) removal system using PAni/MNP nanocomposites, proving to act as an independent monitoring system, and even more the adsorbent on the composites could be removed and the recyclability of the material was also investigated.