Amorphous precursors of LaNbO4 have been prepared by coprecipitation and mechanical alloying. Powder characteristics before and after calcination were studied by thermogravimetric analysis, differential thermal analysis, Fourier transform-infrared spectroscopy and X-ray diffraction, and the crystallographic changes during thermal treatment were documented by high-temperature X-ray diffraction. The tetragonal structure was stabilized at room temperature for the mechanically alloyed product; cells dimensions were determined from the X-ray diffraction patterns and volume change between monoclinic and tetragonal phase was evaluated and is discussed.