The application of cellulose hybrid biocomposites filled with calcium carbonate has attracted wide attention in packaging and other fields in recent years. In this study, regenerated cellulose (RC) films filled with calcium carbonate were successfully prepared by dissolution, regeneration, and in situ precipitation of CaCO3. The optical, mechanical, physical, and chemical properties of biocomposites were examined by UV-visible spectroscopy, tensile testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analyses (TGA). The results showed that RC films with different CaCO3 contents exhibited good flexibility, optical properties, mechanical strength, and thermal stability. The RC biocomposite filled with calcium carbonate showed a tensile strength of 84.7 ± 1.5 MPa at optimum conditions. These RC biocomposites filled with CaCO3 may find application in packaging.