The influence of base pressure, Pb, on physical properties of FeMn exchange biased spin-valve films was studied by varying Pb over two decades from 3×10−8 to 7×10−6 Torr. Giant magnetoresistive value shows a slight increase with increasing Pb until a large decrease occurs at Pb>3.3×10−6 Torr. Exchange bias field and blocking temperature remain constant in the base pressure range between 3×10−8 and 5×10−7 Torr before a large reduction appears. Our results indicate an upper limit for base pressure, Pbu≈5×10−7 Torr, above which significant spin-valve performance modification and deterioration in the crystallographic texture begin as a result of the contamination both at the ferromagnetic/antiferromagnetic interface and in the bulk of FeMn layer.