The coordination of Ni2+ ions in the dehydrated and dealuminated zeolite Y samples were studied by solid-state UV-vis diffuse reflectance spectroscopy. A solid-state dealumination method was employed for preparation of two successively dealuminated zeolite Y using crystalline (NH4)(2)SiF6. Both solid-state and aqueous ion exchange methods were used to prepare nickel-containing zeolite samples. In the dehydrated zeolite samples, nickel cations are located in both regular and distorted tetrahedral symmetries. Their coordination may change from four to five upon adsorption of water molecules following the removal of sample cell from the helium purge system. The spectrum of the dehydrated nickel-containing sample which the zeolite Y was subjected to one step dealumination shows preference for five or six coordinated nickel cations. The spectrum of nickel-containing zeolite sample subjected to a further second step of dealumination is more broaden and does not give reliable data on the coordination of nickel. (C) 2008 Elsevier B.V. All rights reserved.