Crystals of KLaP4O12 have been synthesized by flux technique and characterized by single-crystal X-ray diffraction. This material crystallizes in the orthorhombic Cmc2(1) space group with lattice parameters: a = 8.547(3) angstrom, b = 11.668(1) angstrom, c = 13.351(2) angstrom, V = 1331.4(5) angstrom(3) and Z = 4. The crystal structure has been refined yielding a final R(F) = 0.015 and wR(F-2) = 0.039 for 1303 independent reflections. The three-dimensional framework with intersecting tunnels of KLaP4O12 can be regarded as a succession of alternated [P4O12](4-) anionic and K+, La3+ cationic layers parallel to the (a and b) plane which are centered by the planes z = 0, 1/2 and 1/4, 3/4, respectively. The title compound has been also characterized by different physico-chemical techniques: IR, NMR and. CI spectroscopies and DTA-TGA-DSC thermal analysis. (c) 2007 Elsevier Ltd. All rights reserved.