This work gives an in-depth investigation on the fabrication, characterisation and performance improvement of intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on gadolinia-doped ceria (GDC) electrolyte material. To achieve high-performance IT-SOFCs, the sintering behaviour and electrical properties of GDC electrolytes were studied; the electrochemical performance of (La,Sr)(Co,Fe)O3 (LSCF) and LSCF-GDC cathodes was optimised; a novel (Ba,Sr)(Co,Fe)O3 (BSCF) cathode material was synthesised; and also, a novel spray-copressing process has been developed for fabricating anode-supported thin film GDC electrolyte. With the optimised LSCF-GDC or novel BSCF cathode, single cells base on thin film GDC electrolyte demonstrated encouraging and impressive power outputs in the intermediate-temperature range. In addition, to suppress the electronic conduction in the GDC electrolyte, YSZ film was introduced to the GDC electrolyte cell as an electronic blocking layer. Thin films of YSZ/GDC bilayer electrolyte were successfully fabricated on the anode substrate using a wet ceramic cofiring process.