Laser ablative technology was used to prepare monodisperse nanoparticles (<10 nm in diameter) of lead zirconate titanate (PZT) and strontium bismuth tantalate (SBT). Laser ablation of a ceramic target in oxygen ambience produced amorphous and irregularly-shaped nanoparticles of either PZT or SBT. A subsequent on-line thermal treatment performed on the nanoparticles dispersed in the gas phase brought about compaction and crystallization of the nanoparticles without additional particle growth. It was found that the amorphous PZT nanoparticles began to crystallize above 600°C, and they became a perovskite structure at 900°C. In contrast, the SET nanoparticles began to crystallize at around 800°C. The crystallized nanoparticles were then size-classified by a differential mobility analyzer to yield monodisperse, highly pure, and single-crystalline nanoparticles of PZT and SBT.