The inclusion complexation of comblike poly(ethylene oxide) grafted polymers, P(PEOMA)s, with a-cyclodextrin (alpha-CD) was studied. The grafted polymers were prepared by atom transfer radical polymerization (ATRP) of the macromonomers containing poly(ethylene oxide) (PEOMA) of different molecular weights (M-n = 300, 475, and 1100). The grafted polymers that were made from the macromonomers of M. 1100 and Mn 475 formed crystalline inclusion complexes (ICs) with alpha-CD, while the P(PEOMA) from the PEOMA of molecular weight Mn 300 failed to form ICs with alpha-CD. Furthermore, when the side chain length of the grafted polymers decreased, the time to form inclusion complexation with alpha-CD extended as well as the yields of the inclusion complexes ICs decreased significantly. X-ray diffraction (XRD) data indicated that the obtained ICs have a channel-type crystalline structure. The formation of ICs was further confirmed by differential scanning calorimetry (DSC) and C-13 CP/MAS NMR analysis. The stoichiometry determined by H-1 NMR indicated that the ratio of EO unit to alpha-CD of the resulted ICs is higher than 2:1 (a ratio that was expected from the ICs of linear PEO and alpha-CD). This can be explained that, for the ICs formed between the grafted polymers and alpha-CD, the spatial hindrance of the side chains and bulky size of threaded CD rings prevent the complete coverage of the EO units with CD.