The behaviors of the ionic hydration in nanopore are of both biological and chemical interests. Using carbon nanotube (CNT) as the 1-D nanopore model, we investigated the effect of the modified groups (CO) anchoring on the pore inner wall on the hydration of Li+, Na+ and K+ with molecular dynamics simulation. The structures of the water molecules around the cations confined in the modified CNTs were compared with their counterparts in the pristine CNTs. Among the three cations, the sequence of the sensitivity for the spatial and orientation distributions of the water molecules in the first coordination shells is: K+>Na+>Li+. The same modification results in the opposite effects for the ionic hydration inside the (10, 10) and (8, 8) CNTs. Inside the (10, 10) CNT, the modification enhances the ionic hydration, whereas inside the (8, 8) CNT, the ionic hydration is weakened by the modification of CNT wall. (C) 2010 Elsevier B.V. All rights reserved.