Biomaterials composed of food polysaccharides are of great interest for future biomedical applications due to their great biocompatibility, tunable mechanical properties, and complex architectural designs that play a crucial role in the modulation of cell adhesion and proliferation. In this work, a facile approach was designed to obtain novel 3D alginate-CaCO hybrid hydrogel particles in situ. Controlling the gel concentration from 3 to 20 mg·mL allows us to control the alginate-CaCO hydrogel particles' size and density (size variation from 1.86 to 2.34 mm and density from 1.22 to 1.29 mg/mm). This variable also has a considerable influence on the mineralization process resulting in CaCO particles with varied sizes and amounts within the hydrogel beads. The measurements of Young's modulus showed that the inclusion of CaCO particles into the alginate hydrogel improved its mechanical properties, and Young's modulus of these hybrid hydrogel particles had a linear relationship with alginate content and hydrogel particle size. Cell experiments indicated that alginate-CaCO hybrid hydrogel particles can support osteoblastic cell proliferation and growth. In particular, the amount of hydroxyapatite deposition on the cell membrane significantly increased after the treatment of cells with hybrid hydrogel particles, up to 20-fold. This work offers a strategy for constructing inorganic particle-doped polysaccharide hybrid hydrogel scaffolds that provide the potential to support cell growth.