In this paper, spherical calcium carbonate (CaCO3) with ordered lamella nanostructure was prepared by using regenerated silk fibroin (RSF) as a crystal modifier via compressed CO2. The crystal morphology could be tuned from lens-like to spherical by altering RSF concentration, reaction time, and temperature. Time-resolved experiments showed that the lamellas were formed by several nanoparticles’ aggregation and orientation. Amorphous calcium carbonate (ACC) was seized in the early stage, which would transform to vaterite in a short period. And the dissolution–recrystallization process of CaCO3 was found in a later stage, which was consistent with Ostwald ripening, resulting in the decrease of lamella thickness and the release of RSF that was absorbed in the crystal. Finally, a possible mechanism for the formation of spherical CaCO3 crystal was proposed.

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