Most pharmaceutical manufacturing processes include a series of crystallization processes to obtain the product of the desired properties. The operating conditions of the crystallization process determine the physical properties of the products such as the crystal purity, shape, and size distribution. After the search and selection of suitable solvent and anti-solvent, batch crystallization of fosamprenavir calcium was performed with the addition of water at 25 ° C and 30 ° C. The effect of the addition of a different volume fraction of antisolvents on the granulometric properties of fosamprenavir calcium crystals was investigated. Fosamprenavir calcium is used as a prodrug of amprenavir in the fight against human immunodeficiency virus. It was found that increasing the volume fraction of anti-solvent leads to a decrease in the concentration of the solution, the concentration reaches very low values at about 30% water content, from which it could be concluded that most of the salts were separated from the solution. Based on the images obtained by light microscopy and the crystal size distribution determinated using laser disfraction method, an increase in the proportion of smaller crystals with an increase in the volume fraction of antisolvents was established. Also, it was shown that the crystals obtained in the experiments at a higher temperature (30 ° C) were larger, and the proportion of smaller particles (in the range of about 1 μm) was significantly smaller. Kinetic constants: the crystal growth rate constant kg and the crystal growth order g were determined by the potential equation, and the presence of polymorphic forms in the samples was determined by analysis of DSC-curves obtained by differential scanning calorimetry (DSC).