The effect of the mobility of ligands (maltose groups) in the polyrotaxanes (pRXs) on the structure ofthe surrounding water molecules was investigated. Raman spectra of collective OH stretching vibrationof water molecules in aqueous solutions of maltose-pRX conjugates with different α-cyclodextrin (α-CD)threading on a poly(ethylene glycol) (PEG) chain was measured. The mobility of maltose groups wasestimated by measuring the relaxation time T2 of the C1 protons in maltose groups bound on α-CD by NMRexperiment. A positive correlation between the Raman intensity of the collective band and the relaxationtime T2 was obtained. This result indicates that the degree of order of the water clusters is higher as themobility of maltose groups increases in these conjugate solutions. It is suggested that rapid motion ofmaltose groups in the pRX conjugate can contribute to preserving ordered structure of the bulk waterclusters.