The soluble protein related to shell regeneration (SPSR) plays an important role to repair the damaged shell. In this study, the SPSR was used as a biocatalyst to control the crystal growth and morphology during in vitro CaCO 3 crystallization. Anion exchange fast protein liquid chromatography (FPLC) was applied to separate the SPSR constituents. Each fraction from purification of the SPSR was subjected to CaCO 3 crystallization to identify the fraction's effect on controlling the CaCO 3 crystal morphology. CaCO 3 crystallization experiments were performed by mixing solutions of CaCl 2 and purified SPSR in the presence of vaporized (NH 4 ) 2 CO 3 . The morphology of the CaCO 3 crystals was characterized by field emission scanning electron microscopy (FE-SEM). The synthesized CaCO 3 was characterized by Fourier transform infrared spectroscopy (FT-IR) to reveal the type of crystals formed. In vitro CaCO 3 crystallization process showed the effect of SPSR on the morphology change of CaCO 3 crystals. We identified a condition for rapid crystal growth and specific morphology of CaCO 3 in the presence of SPSR. Thus, our study confirms that SPSR governs CaCO 3 crystallization and influences the observed crystal morphology.