LaPO4:Ln(3+) (Ln(3+) = Ce3+, Tb3+) and LaPO4:Ce3+,Tb3+/LaPO4 core/shell nanowires have been synthesized on a large scale through a direct precipitation in a water-based system under moderate conditions without the assistance of any surfactant, catalyst, or template. The diameters of the obtained nanowires are about 15 nm, and the lengths range from a few hundred nanometers to several micrometers. The influences of the solution acidity, reaction time, and proportion of ethanol to water on the final products were investigated in detail. It was found that the lengths of nanowires can be efficiently controlled by adjusting the reaction conditions. The formation mechanism of the products is proposed on the basis of time-dependent experiments as well as the crystal structure of the products. The luminescent properties of the products were also studied. A LaPO4 shell on the LaPO4:Ce3+,Tb3+ nanowires can greatly increase the intensity of the product, and the thickness of the shell also has an important effect on the intensity of the product. The method is a novel and facile route for the synthesis of one-dimensional lanthanide phosphates.