The objective of this work is to enhance the adsorption efficiency of chitosan toward As(III), a highly toxic and predominant arsenic species in groundwater, and to increase its antimicrobial activity at neutral pH values, the pHs of natural waters. Therefore, Cu-chitosan/alumina nanocomposite was prepared and tested as a new adsorbent for removal of As(III). The prepared adsorbent was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), Fourier transform Infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The modified adsorbent showed a more porous surface morphology compared to neat chitosan. The results of FTIR, EDX and XRD revealed that Cu2+ ions form a complex with amine groups on the chitosan surface. The adsorption behavior of As(III) on Cu-chitosan/nano-Al2O3, chitosan/nano-Al2O3 and neat chitosan was investigated using adsorption kinetics and isotherm studies at room emperature. The adsorption data for three types of adsorbents were fitted well by Freundlich model. The kinetic data showed good compliance with a pseudo-second-order kinetic model. The modified adsorbent exhibited a higher adsorption capacity and initial adsorption rate. Antimicrobial activity of the adsorbents was studied by minimum inhibitory concentration (MIC) method. The antimicrobial activity of Cu-chitosan/nano-Al2O3 was much higher than that of chitosan/nano-Al2O3 and neat chitosan. (C) 2015 Elsevier B.V. All rights reserved.