Solid oxide fuel cell electrolytes are currently manufactured from zirconia. This is due to its high ionic conductivity and mechanical strength. However, a disadvantage of zirconia is the high temperatures required for efficient operation, greater than 900C for cells not utilising thin supported electrolytes. A study to characterise the properties of an alternative composite solid electrolyte, based on a gadolinia doped ceria matrix surrounding yttria stabilised tetragonal zirconia particles is presented. Composite samples produced using 1, 2, 5, 10 and 20 wt% zirconia particles were characterised using a range of different experimental techniques including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, mechanical testing and impedance spectroscopy. Results showed a lowering in flexure strength of the experimental composite samples with the addition of particles. It is considered that the particles acted as regions where cracks could initiate.