Poly(ethylene glycol) (PEG)‐interlocked hydrogels were prepared by linking the PEG with α‐cyclodextrins (α‐CDs) threaded onto a PEG chain having ester linkages at the terminals (hydrolyzable polyrotaxane). These hydrogels were examined to clarify the effect of ionic strength of phosphate buffers, pH, and the addition of ethanol on erosion time in relation to inclusion states of α‐CDs with the ester linkages. The most characteristic phenomenon of the hydrogel erosion was observed in an ethanol/PBS cosolvent system: the time to reach the complete erosion time was shortened with decreasing water content. NMR analysis revealed that the ester linkages were exposed to the aqueous environment due to the aggregation of α‐CDs. These results suggest that the movement of α‐CDs in the polyrotaxanes from the terminal ester region to the another region gives the ester linkages a chance to interact with water.
