A novel glass-mica composite seal was developed based on a previously reported concept of "infiltrated" mica seals for solid oxide fuel cells. Ba-Al-Ca silicate sealing glass powder and Phlogopite mica flakes were mixed at glass volume fractions of 10-50vol.% to make the glass-mica composite seals. The seals were leak tested for short-term thermal cycle stability as a function of glass volume fraction. Composite seals with 10 and 20vol.% glass were also leak tested under compressive stresses from 3 to 100 psi and helium pressures of 0.2 or 2 psi. Post-mortem microstructure analyses were used to characterize the fracture (leak path) of the glass-mica composite seals and were related to the high temperature leakages. Open circuit voltage tests on dense 8YSZ electrolyte with the glass-mica composite seal showed very good thermal cycle stability over 250 cycles with minute (< 1%) voltage drop. (c) 2005 Elsevier B.V. All rights reserved.