This study explored the adsorption capacity of diethylene triamine grafted dialdehyde nanocrystalline cellulose (DETA-g-DA-NCC) for As (III and V) removal from aqueous solution. Nanocrystalline cellulose (NCC) was selectively oxidized using sodium periodate followed by grafting of diethylene triamine (DETA) to obtain their amine derivatives in 80-85% yield. A corresponding increase in carbonyl content of the dialdehyde nanocrystalline cellulose (DA-NCC) with the increase in oxidant concentration was measured by titrimetric analysis and was evidenced by FT-IR spectroscopy. Morphological integrity and crystallinity of the NCC were maintained after the functionalization as studied by AFM, SEM and XRD, respectively. The effect of various operational parameters such as arsenic ion concentration, pH, biosorbent dosage and time was investigated using batch experiments and found that DETA-g-DA-NCC can be used as a cost effective biosorbent for decontamination of arsenic. The experimental data were analyzed by Langmuir, Freundlich, Temkin and Dubinin-Redushkevich (D-R) models of sorption. The sorption isotherm data were fitted well to Langmuir isotherm. The kinetic data were fitted very well in the pseudo-second-order kinetic model and suggested that the chemisorptions were the rate-limiting step. The results indicate that there is significant potential for DETA-g-DA-NCC as a biosorbent for arsenic removal [As(III) 92.84% and As(V) 97.86%] from aqueous solutions. (c) 2015 Elsevier B.V. All rights reserved.