Fluorescent rare earth nanophosphates (La0.95Eu0.05PO4, Ce0.9Tb0.1PO4, and La0.4Ce0.45Tb0.15PO4) were synthesized by reacting the corresponding nitrates exclusively inside PO43- loaded poly(styrene sulfonate)/ poly(allylamine hydrochloride) polyelectrolyte capsules of 2.4 mum diameter at room temperature. Crystallization conditions inside the polyelectrolyte capsules lead to the fabrication of crystalline nanoparticles with high fluorescence yield without additional thermal treatment. The fluorescence of these nanoparticles is stable at low and neutral pH. The fluorescent rare earth nanophosphates, fabricated inside polyelectrolyte capsules, were characterized by TEM, SEM, and XRD techniques and fluorescence spectroscopy. Resulting nanophosphates are nanorods ca. 15 nut long and 4 urn in diameter, and they are formed near the inner side of the capsule wall.