The properties of dual-synthetic antiferromagnet (DSAF) structure Co90Fe10(5 nm)/Ru(x nm)/Co90Fe10(3 nm)/Ru(y nm)/Co90Fe10(5 nm) (in which x=0.45 y=0.45; x=0.45 y=1; x=1, y=1) were studied. The effect of DSAF structure on giant magnetoresistance (GMR) single spin-valve (SPV) structures was also studied. The study shows that the properties of DSAF are better than those of the conventional synthetic antiferromagnet Co90Fe10(5 nm)/Ru(0.5 nm)/Co90Fe10(3 nm). We demonstrated that the DSAF structure as a pinned layer dramatically enhances the GMR ratio in single SPV films at room temperature.