We have found in studying Cu-doped barium sodium niobate (BNN) that adjusted appropriately the ingredient composition of BNN within it's tungsten structure forming limits, the Cu-doped BNN synthesized in air has the regularity that Cu in BNN can form naturally Cu+ and Cu2+. The valence state of Cu was determined by X-ray photoeletron spectra (XPS) analysis. The occupancy site of Cu ions in the Cu-doped BNN crystals structure and colour of the Cu-doped BNN crystal are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.