The enhancement in bioavailability of the drugs is one of the most important concerning aspects of the pharmaceutical industries. Preparation of nanoparticles or microparticles of these drugs is the newest formulation strategies. The size and morphology of a drug are affecting several essential pharmaceutical properties. In general, the drug delivery system needs narrow particle size distribution with regular particle shape, particularly, an engineered drug particles to meet biopharmaceutical and processing needs. An antisolvent crystallization technique is being used to prepare nanoparticles or microparticles for poorly water soluble drugs at research scale. This method has an ability to change the solid-state properties of pharmaceutical substances including the modification of crystal formation and particle size distributions. Therefore, various operating variables and their effect on the particle size of poorly water soluble drugs in an anti-solvent crystallization have been reviewed.