This chapter reports our SR measurements of the spin-ladder cuprates Srn-1Cun+1O2n (n=3, 5). The measurements have revealed contrasting magnetic behaviors between the `2-leg' (n=3) and the `3-leg' (n=5) spin-ladder materials, which qualitatively agree with the theoretical predictions. The results presented in this chapter, in addition, provide a good example of how SR detects the existence/absence of magnetic order.