The present invention generally relates to preparation methods of nanoparticles or nanocrystals of narrowly distributed particle sizes of a poorly water soluble material. In particular, this invention is an effective integration of the bottom-up and top-down preparation methods of nanoparticles and nanocrystals of a poorly water soluble material or active pharmaceutical ingredient into a single process, which affords an efficient and simple process with a product of improved delivery and therapeutic effects.
