A series of inclusion complexes of poly(ethylene oxide)-block- poly(propylene oxide)-block-poly(ethylene oxide) (PEO- b -PPO- b -PEO) with β -cyclodextrin (β -CD) was prepared. Their formation, structure, and dynamics were investigated by solution two-dimensional rotating-frame Overhauser effect spectroscopy (2D ROESY) and one-dimensional (1D) and 2D solid-state 13C NMR. The inclusion complexes between the PEO- b -PPO- b -PEO copolymers and the β -CDs were formed in aqueous solution and detected by 2D ROESY. The high efficiency of cross polarization and spin diffusion experiments in C 13 solid-state NMR showed that the mobility of the PPO blocks dramatically decreases after β -CD complexation, indicating that they are selectively incorporated onto the PPO blocks. The hydrophobic cavities of β -CD restrict the PPO block mobility, which is evidence of the formation of inclusion complexes in the solid state. The 2D wide-line separation NMR experiments suggested that β -CDs only thread onto the PPO blocks while forming the inclusion complexes. The stoichiometry of inclusion complexes was studied using H1 NMR, and a 3:1 (PO unit to β -CD) was found for all inclusion complexes, which indicated that the number of threaded β -CDs was only dependent on the molecular weight of the PPO blocks. 1D wide angle x-ray diffraction studies demonstrated that the β -CD in the inclusion complex formed a channel-like structure that is different from the pure β -CD crystal structure.