Low-molecular-weight liquid poly(ethylene glycol) (PEG) spontaneously forms an inclusion compound (IC) when combined with alpha-cyclodextrin (alpha-CD) powder at room temperature. This process can be followed with wide-angle X-ray diffraction (WAXD). The WAXD data shows that the alpha-CD crystals undergo a solid-state crystal-crystal transformation from the cage to the channel crystal structure upon IC formation over a period of about 8 h. The time dependence of the 2theta = 20degrees alpha-CD channel structure X-ray peak can be described by a simple first-order kinetic model. The effects of changing the temperature, PEG:alpha-CD molar ratio, PEG molecular weight, and vacuum-drying the CD have been studied. The barrier opposing the PEG inclusion-induced solid-state transformation of a-CD from the cage to the channel crystal structure appears to be dominated by changes in the packing/interactions of alpha-CDs, rather than the loss in the conformational entropy experienced by the PEG chains during the inclusion process.