We report a method of polymer alloying by inclusion complex formation of a helical synthetic polymer. By introducing C-60 units at the ends of poly(dimethylsiloxane) (PDMS) and utilizing inclusion complex formation between the C-60 units and helical syndiotactic poly(methyl methacrylate) (st-PMMA), we succeeded in preparing an alloy of polymers that are originally immiscible. The encapsulation of PDMS-C-60 within the st-PMMA helical cavity occurred during the gelation of st-PMMA with toluene in the presence of PDMS-C-60. Although the functionality of C-60 in the as-prepared polymer was relatively low, the completely C-60-end-capped polymers can be isolated by inclusion complex formation. A brown-colored st-PMMA/PDMS-C-60 inclusion complex film was obtained without macroscopic phase separation by evaporating the solvent from the gel. The st-PMMA/PDMS-C-60 film showed improved thermal properties owing to the crystalline structure of the inclusion complex, which retained the homogeneity up to its melting point.