Poly(oxyethylene) (PEO) containing a 4,4 '-diaminodiphenylmethane moiety with thiol groups at the terminals (1SH) and its inclusion complexes with gamma- and, beta-cyclodextrins (gamma- and beta-CDs) (2SH and 3SH) were prepared. H-1 NMR spectroscopy indicated that the two molecules of 1SH were bundled with gamma-CD through intermolecular interaction in 2SH while the only one molecule was included with beta-CD in 3SH. The polymer 1SH and the complexes 2SH and 3SH were chain-extended by disulfide linkage formation through oxidation reaction (1SS, 2SS, and 3SS, respectively). All of the complexes were confirmed by using gel permeation chromatography and viscosity measurement. Significant increases in the viscosity were observed for 2SH and 2SS, compared with 1SH, 3SH and 1SS, 3SS, respectively. It is suggested that the double-stranded inclusion complexation of the PEO chains by gamma-CD like the bundling with its cavity acts as a cross-link and contributes to network formation.