Ellipsoidal nanocrystalline LaPO 4 :Eu has been realized through an aqueous method by using microwave irradiation and microfluidic system. Through this method, we can control the nucleation and growth process. The as-prepared nanoparticles are pure monazite phase and water-dispersible and monodisperse, with a mean diameter of 4nm and length of 6nm. Luminescence data indicate the samples have a strong orange–red emission corresponding to 5 D 0 → 7 F 1 transition. Under the optimized conditions, the quantum yield is 21%. According to MTT assay, the nanoparticles are non-toxic materials and good biocompatibility. Therefore the LaPO 4 :Eu nanoparticles may possess the potential to serve as a luminescent bioimaging probe.