Both Ba24Si100 and Ba24Ge100 with crystallographically identical structure are the superconductors whose critical temperatures are 1.45 and 0.27 K, respectively. Intriguingly, physical properties of the both compounds are extremely different. The observed differences are considered to be associated with Ba rattling motions. We have exemplified such unique motions in terms of x-ray diffraction data using MEM/Rietveld analyses. We present these exotic systems especially focusing on the relation between superconductivity and the rattling phonons.