The crystal structure, sintering characteristics, electrical conductivity and thermal expansion of GdxTi2O7 - delta pyrochlores (1.72 less than or equal to x less than or equal to 2.10) have been studied as potential electrolytes in high-temperature solid oxide fuel cells (SOFC). It was found that the A-site deficiency of GdxTi2O7 - delta with cubic symmetry showed a wide region of 1.72 < x < 2.03. A-site vacancies promoted the sintering characteristics of these materials. Electrical conductivity of the pyrochlores with A-site vacancies was lower than that of GdxTi2O7 in air although the reverse was observed in reducing atmospheres, due to the appearance of electronic conduction. Average linear thermal expansion coefficients of GdxTi2O7 - delta pyrochlores decreased with increasing A-site vacancies. The difference between the TEC in air and in a H-2 atmosphere had a tendency to increase with increasing A-site vacancies.