Inclusion complexes (ICs) of biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate] -poly(ethylene oxide) triblock copolymers with alpha-cyclodextrin (alpha-CD) or gamma-cyclodextrin (gamma-CD) were prepared from aqueous medium. The ICs were characterized by XRD, DSC, C-13 CP/MAS NMR, H-1 NMR, FTIR, and TGA. The results of XRD and C-13 CP/MAS NMR indicated that the ICs formed channel structure, and the alpha-CD or gamma-CD molecules in the ICs adopted a more symmetric conformation compared with their uncomplexed states. As to the triblock copolymers, while the poly(ethylene oxide) blocks were included in the channel structure, the poly [(R)-3-hydroxybutyrate] block was partially threaded by alpha-CD or gamma-CD, which was confirmed by the results of XRD, DSC, H-1 NMR, and FTIR. The formation of ICs led to an increase in the thermal stability of both cyclodextrins and the triblock copolymers.