NdPO₄•nH₂O nanorods with a pure hexagonal and monoclinic phase were controlled synthesized through a hydrothermal route at low temperature. By simply increasing the molar ratio of PO₄/Nd, pure monoclinic NdPO₄can be obtained at lower temperature of 180 °C. Furthermore, NdPO4•nH2O nanorods can be assembled into flower- or bundle-shape. The reactant molar ratio played key roles in the formation of the products with different morphologies and structures. The possible formation mechanism for NdPO4 nanorods with different morphologies and structures was discussed. In addition, low-cost preparation of NdPO4 nanorods could be achieved through cycling use of phosphoric acid. Furthermore, this synthesis strategy will open a novel approach to rare earth phosphates with multiple structures.