Thin films of gadolinium-doped ceria (GDC) nanoparticles were fabricated as electrolytes for low-temperature solid oxide fuel cells (SOFCs) by combining electrophoretic deposition (EPD) and the successive ionic layer adsorption and reaction-air spray plus (SILAR-A+) method. The Ce<sub>1-<i>x</i></sub>Gd<i><sub>x</sub></i>O<sub>2-<i>x</i>/2</sub> solid solution was synthesized using hydrothermal (HY) and solid-state (SS) procedures to produce high-quality GDC nanoparticles suitable for EPD fabrication. The crystalline structure, cell parameters, and phases of the GDC products were analyzed using X-ray diffraction. Variations in oxygen vacancy concentrations in the GDC samples were achieved through the two synthetic methods. The ionic conductivities of pressed pellets from the HY, SS, and commercial G<sub>0.2</sub>DC samples, measured at 150 °C, were 0.6 × 10<sup>-6</sup>, 2.6 × 10<sup>-6</sup>, and 2.9 × 10<sup>-6</sup> S/cm, respectively. These values were determined using electrochemical impedance spectroscopy (EIS) with a simplified equivalent circuit method. The morphologies of G<sub>0.2</sub>DC thin films prepared via EPD and SILAR-A+ processes were characterized, with particular attention to surface cracking. Crack-free GDC thin films, approximately 730-1200 nm thick, were successfully fabricated on conductive substrates through the hybridization of EPD and SILAR-A+, followed by hydrothermal annealing. EIS and ionic conductivity (1.39 × 10<sup>-9</sup> S/cm) measurements of the G<sub>0.2</sub>DC thin films with thicknesses of 733 nm were performed at 300 °C.