PbTe, a narrow (direct) band gap semiconductor, has a relatively low phase transition pressure and promising pressure-dependent behavior for many important applications.Monodisperse and size-tunable PbTe nanocrystals (NCs) were prepared using a solutionbased synthetic approach.Using an in-situ synchrotron X-ray diffraction technique, a pressure-induced phase transformation of these PbTe NCs was studied.We observed that the pressure-induced (up to ～20 GPa) phase transformation of PbTe NCs is dependent on their crystal size.