Polyglycidols of tunable degree of branching (DB) have been synthesized via ring-opening multibranching polymerization (ROMBP) of glycidol in the absence of any initiators using heterogeneous double metal cyanide (DMC) catalysts. Semi-branched polyglycidols of low DB (less than 0.3) are obtained using simple solvent-free batch polymerizations, whereas hyperbranched analogues of high DB (more than 0.5) are achieved employing semi-batch (or slow monomer addition) polymerizations. The rate of DMC-catalyzed ROMBPs of glycidol shows the first-order dependences on monomer and catalyst concentrations, suggesting that the ROMBPs proceed via a coordinative mechanism. The formation of propagating species and the resultant microstructural units are clarified using a conversion versus time analysis in the NMR-scale.