To overcome the increased processing of eggshell waste in East Java, Indonesia, the important solution is to synthesize chicken eggshells into calcium carbonate. The process of synthesizing eggshells into calcium carbonate is carried out by a mechanochemical process using a ball milling machine for 10 h and the sintering time for 120 min at a temperature of 900, 1000, 1100, and 1200 °C. The results of the eggshell synthesis were characterized using X-ray Diffraction, SEM, Raman spectroscopy and FTIR. Those characterizations aimed to obtain the result of phase identification, morphology, physicochemical, and functional group of calcium carbonate. From the phase identification, calcium carbonate obtained from eggshell sintered 1000 °C shows the single-phase triangular structure with agglomeration and spherical morphology. The physicochemical results show that phonon interaction of calcium carbonate obtained from eggshell sintered at 1200 °C has the highest intensity at Raman shift 1083 cm^‒1 which indicates the C‒O symmetric stretching band. The functional group of calcium carbonate shows from FTIR results at 3642, 2987, 2508 cm^‒1 for O‒H bond, and 1790, 1507 cm^‒1 for C‒H bond, and 874, 712 cm^‒1 for calcite bonds respectively.