Cocrystals consist of two molecules bonded together in a single crystal lattice giving rise to wide applications including improving solubility of poorly soluble pharmaceuticals. Cocrystallization reaction occurs in the oily phase of liquid–liquid phase separation (LLPS) after it is mixed with coformers. Indomethacin–saccharin cocrystal formation was monitored in situ, and the kinetics of crystallization were determined. The crystallization rates show that the process can be proposed to prevent unwanted oily phase formation during LLPS.