The definition and an X-ray determination method of the degee of preferred orientation of ferroelectric ceramics with layer type structure after hot-pressing procedure are presented. The degree of preferred orientation can be obtained by merely determining the ratio of diffraction intensity of any one or more (00l) lines before and after hot-pressing procedure. Taking the mixed bismuth oxide compound with layer type structure PbBi4Ti4O15 as an example the suitability of this method has been proved.