A current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin valve using epitaxial layers of Co2 FeAl0.5 Si 0.5 (CFAS) Heusler alloy as ferromagnetic electrodes is reported. A multilayer stack of Cr/Ag/CFAS/Ag/CFAS/ Co75 Fe25 / Ir22 Mn78 /Ru was deposited on a MgO (001) single crystal substrate. Epitaxial growth of the Cr, Ag, and CFAS layers in the (001) orientation up to the top CFAS layer was confirmed. Large MR ratios of 6.9% at room temperature and 14% at 6 K were observed for the CPP-GMR device. High spin polarization of epitaxial CFAS is the possible reason for high MR ratios.