The effect of 18-crown-6 ether (18C6) in the anionic cyclopolymerization of 1,2:5,6-dianhydro-3,4-di-O-methyl-D-mannitol (1) using potassium tert-butoxide (t-BuOK) was studied. The addition of 18C6 did not affect the regio-and stereoselectivity in the polymerization of 1, and the resultant polymer was (1-->6)-2,5-anhydro-3,4-di-O-methyl-D-glucitol (2). The complexation of t-BuOK with 18C6 increased the initiator efficiency from 0.3 to 1.0, which was accompanied by enhancement of the apparent polymerization rate. The rate constant ratios of the transfer reaction to the propagation (k(tr)/k(p)) in the systems with and without 18C6 were 1 order of magnitude lower than the value in the polymerization of monoepoxides. The "living" nature of the t-BuOK/18C6 initiating system was evaluated by the two-step monomer resumption experiment.