Eu 3+ -doped GdPO 4 nanoparticles were synthesized by a straightforward combustion method using urea as fuel and metal nitrates as precursors. Structures, morphologies and photoluminescent properties of the synthesized samples were studied by X-ray diffraction, scanning electron microscopy and photoluminescent spectroscopy. There are two types of crystal structures formed during the annealing process: hexagonal GdPO 4 .H 2 O and monoclinic GdPO 4 . The former can be found at low annealing temperatures (300-500 °C) while the latter can be obtained at higher annealing temperatures (700-900 °C). The average diameters for nanoparticles are 20-30 nm. Under the excitation at 273 nm, both GdPO 4 .H 2 O:Eu 3+ and GdPO 4 :Eu 3+ powders showed red emission bands originating from the 5 D 0 -7 F J (J = 1, 2, 3 and 4) transitions of Eu 3+ . Their PL intensity and crystal structures exhibit a similar behavior as a function of the annealing temperature.