Lanthanum silicate oxyapatite, La10Si6O27 is successfully synthesized by a water-based gel-casting technique. The effect of calcination and sintering temperatures on the conductivity is investigated in detail in the temperature range between 300 and 800 degrees C by the impedance spectroscopy. The highest oxygen ion conductivity is 1.50 x 10(-3) Scm(-1) at 500 degrees C and 3.46 x 10(-2) Scm(-1) at 800 degrees C for an apatite electrolyte sintered at 1650 degrees C, which is one order of magnitude higher than that synthesized by the conventional solid state reaction route under the same sintering conditions. The thermal expansion coefficient (TEC) of the as-synthesized apatite is 9.7 x 10(-6) K-1. A solid oxide fuel cell using La10Si6O27 as an electrolyte shows an open circuit potential of 1.06V and power output of 7.89 MW cm(-2) at 800 degrees C. The results demonstrate the potential of the silicate oxyapatite materials synthesized by the gel-casting as an alternative electrolyte in solid oxide fuel cells. (C) 2008 Elsevier B.V. All rights reserved.