This paper describes a general hydrothermal route for the synthesis of a series of rare-earth orthophosphates, LnPO(4)center dot xH(2)O (Ln=La, Y, Ce, Sm, Gd, Tb, Dy, Er, and Yb), with a mean diameter of similar to 100 nm. The procedure involves the formation of homogeneous, transparent, metal-citrate-ethylenediamine tetraacetic acid (EDTA) gel precursors using both citric acid and EDTA as the complexing agents, followed by hydrothermal mineralization to yield the final LnPO(4)center dot xH(2)O nanocrystallites. Techniques of X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscope have been used to characterize the as-synthesized LnPO(4)center dot xH(2)O nanocrystals. Furthermore, photoluminescence (PL) characterization of the Eu3+-doped LnPO(4)center dot xH(2)O nanocrystals was carried out. The results indicate that the PL property changes considerably with the ionic radii of the rare-earth elements.