We studied the interfacial spin-dependent scattering in Co2Fe(Al0.5Si0.5)/Ag/Co2Fe(Al0.5Si0.5) current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A large contribution of the interfacial scattering was evidenced by the small interfacial resistance of ARF/N ∼0.25 mΩμm2 and the large interfacial scattering spin asymmetries of γ ∼0.93 at 14 K and ∼0.77 at 290 K. Moreover, the insertions of 1 nm thick Co2Fe(Al0.5Si0.5) layers at Co50Fe50/Ag interfaces effectively improved the output of CPP-GMR. Thus, Ag is considered to be a suitable spacer material for the Co2Fe(Al0.5Si0.5) Heusler alloy with a good band matching.