A particle size dependent modification in crystal structure of submicron KNaNb2O6 powders was observed for the first time by X-ray diffraction coupled with Raman spectroscopy. We saw a clear correlation between crystal size and crystallographic structure. Particles larger than 200 nm in diameter consisted of a perovskite type monoclinic phase whereas particles smaller than 200 nm were found to be triclinic. The lattice parameters were refined for both modifications and possible space groups defining the modifications were given. (C) 2004 Elsevier B.V. All rights reserved.