The coordination changes of Co2+ in CoNaY/NaOHs, prepared by cobalt ion-exchange and treatment with NaOH, during dehydration at various temperatures have been investigated by UV/VIS diffuse reflectance spectroscopy. After dehydration of CoNaY/NaOHs at 473 K, the DRS bands show the formation of mixed cobalt oxide species interacted with lattice oxygen. This mixed cobalt oxide species interacted with lattice oxygen decompose during further dehydration at 673 K. The strong intensities of the bands at 660, 575 and 530 nm after dehydration of CoNaY/NaOHs at 873 K indicate that a considerable amount of the cobalt ions remains in the sodalite cage with tetrahedral coordination even after dehydration at 873 K.