Lanthanum phosphate (LaPO4) powder has been synthesized by direct liquid-liquid reaction of La(NO3)(3)center dot 6H(2)O and H3PO4. The as-received powder has been heat treated at various temperatures (100, 600, 800, 1000, or 1200 degrees C). The phase composition and microstructure of the powder have been characterized by XRD, SEM, HRTEM, and FFT. The anisotropic growth mechanism, phase transition from hexagonal to monoclinic structure, and shape evolution details of LaPO4 nanoparticles are discussed. The results show that the phase composition and microstructure of the powder depend on the heat treatment temperature. The hexagonal phase converts to a monoclinic structure around 600 degrees C. Another consequence of the heat treatment is a change in the shape of the LaPO4 as nanorods are converted into nanograins with increasing heat treatment temperature. Particularly, at 1000 degrees C, the nanorods begin a gradual transition to nanograins. When the temperature is increased to 1200 degrees C, all the LaPO4 nanorods have transformed into spherical LaPO4 nanoparticles with a diameter in the range of 300-500 nm. (C) 2010 Elsevier B.V. All rights reserved.