The electrochemical behavior of rare earth ions (RE3+) doped CaCO3/PEG nanocomposites (RE3+ = 0.08 mol Y, La, and Gd) synthesized via a biomimetic method using dolomite rock as a carbonate source was thoroughly analyzed through XRD, FTIR, UV-Vis-DRS, Band gap, PL, FE-SEM, and HR-TEM analyses. All the prepared products were in rhombohedral structure, and the obtained crystallite size was in the range of 25-23 nm. The average microstrain and dislocation density of the products were also calculated, and the values are 1.33, 1.35, and 1.73 x 10(-3) and 12.69, 13.21, and 22.21 x 10(14) for Y, La, and Gd-doped CaCO3/PEG nanocomposites. The FTIR results revealed the presence of characteristic peaks (477, 479, and 465 cm(-1)), which confirmed that the products were Y, La, and Gd-doped CaCO3/PEG nanocomposites. From the UV-Vis-DRS, band gap, and PL analyses, 0.08 mol RE3+ ions doped CaCO3/PEG nanocomposites demonstrate blue shift absorption and emission values with increasing band gap values (4.50, 4.58, and 4.70 eV). The formation of spherical-shaped morphology was affirmed by FE-SEM and HR-TEM analyses, and the calculated particle size was in the range of 32-26 nm. The pseudocapacitive behavior of 0.08 mol Y, La, and Gd-doped CaCO3/PEG nanocomposite electrodes was confirmed via CV, GCD, and EIS. They showed specific capacitances of 261, 270, and 288 F/g, respectively, at 5 mV/s using a CV curve, with 97% cyclic stability over 1000 cycles. Energy and power density were calculated, and the values are 51.6, 52.6, and 53.4 Wh kg(-1) and 1416.28, 1229.21, and 1221.347 W kg(-1) for Y3+, La3+, and Gd3+ anchored CaCO3/PEG nanocomposites, at 1 A/g respectively.