The first radical end-coupling synthesis of polydimethylsfloxane (PDMS)-gamma-cyclodextrins (gamma-CDs) based polyrotaxane is reported. Conversely to usual chemical way, the radical process leads to fast both controlled size and structure with minimal side reaction while exhibiting very high conversion rate (w/w, 80%). Pure PDMS-gamma-CDs molecular necklaces were successfully isolated by preparative size exclusion chromatography and finely characterized both by 1D/2D/STD H-1 and C-13 NMR and MALDI-TOF mass spectrometry. The observations give dear evidence of the supra molecular assembly synthesis where the filling ratio (gamma-CD/monomer unit) of PDMS chains is as high as 40% of gamma-CDs. Combination of such radical-based coupling supported by detailed analytical characterizations appears at the forefront of a fast, suitable, and easily amenable scaling-up CDs-based polyrotaxane synthesis process.