Spherical agglomerated crystals of ascorbic acid (AA) have been prepared with a trace of polyvinylpyrrolidone (PVP) by a spherical agglomeration method. The process of spherical crystallization has been monitored online with a partide vision and measurement (PVM) probe. The effect of PVP on the metastable zone width of ascorbic acid in aqueous solutions has been characterized by a laser method. Hydrogen bonding interactions between AA and PVP have been identified by Fourier-transform infrared spectroscopy and H-1 nuclear magnetic resonance. Differential scanning calorimetry and powder X-ray diffraction measurements have shown that the prepared spherical crystals still exhibited a crystallin nature. The micromeritic properties, namely flowability, packability, and compressibility, were significantly improved compared to those of the pure drug crystals. In this study, we have explored the mechanism of the spherical crystallization process in the presence of the polymer, and the beneficial effect of the polymer on the micromeritic properties of crystals of ascorbic acid. (C) 2018 Elsevier B.V. All rights reserved.