Gadolinium phosphate, obtained through crystallisation from phosphoric acid solution containing Ca-ions, has been characterised by X-ray diffraction, IR-spectra and scanning electron microscopy methods. The presence of Ca-ions in solution resulted in Ca for Gd substitution coupled with simultaneous HPO42- incorporation in crystalline hexagonal GdPO4.H2O. The HPO42- compensated for the difference in the electric charge between divalent calcium and trivalent gadolinium in the crystallised solid. The amount of Ca in the solid obtained did not exceed 2.5 wt%. Calcium incorporation in gadolinium phosphate caused significant enlargement along the c-axis and less significant contraction along the a-axis of the GdPO4.H2O unit cell. (C) 2004 Kluwer Academic Publishers.