Phase-change Ge-Sb-Te (GST) nanoparticles have been in situ synthesized by a pulsed laser ablation method. Temperature of heat treatment, pressure during ablation, and laser fluence are extensively explored to examine growth behavior of GST nanoparticles. Scanning and transmission electron microscopy are used to study microstructure and phase formation of the nanoparticles. Energy dispersive X-ray analysis is performed to look into chemical composition of the GST nanoparticles. It is found that stoichiometric GST nanocrystals with 5-50 nm of grain size are formed around 200 °C.