Cationic polymerization of vinyl ether (VE) was examined with methanol/metal chloride initiating systems instead of those with the conventionally used VE-protonic acid adduct initiators. With MoCl5, a highly oxophilic metal halide, the polymerization of isobutyl VE (IBVE) using methanol proceeded in a living fashion in the presence of ethyl acetate, although the reaction was not controlled in conjunction with IBVE-HCl adduct. Furthermore, in the methanol-initiated polymerization, the Lewis acids used could be classified mainly into three categories in terms of polymerization behavior: those producing long-lived species (e.g., MOCl5, NbCl5, and ZrCl4), those inducing uncontrolled polymerization (e.g., GaCl3 and FcCl(3)), or those showing no activity at all (e.g., ZnCl2 and InCl3). The matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDT-TOF-MS) spectra of the product polymers and the direct H-1 NMR analysis of the reaction mixtures revealed that the controlled polymerization starts with an exchange reaction between the methoxy group of methanol and the chloride anion of a metal chloride to generate HCl, the true initiator. With some Lewis acids such as NbCl5, the polymerization proceeds only via thus produced C-Cl terminals as dormant species, whereas rapid equilibrium between the C-Cl ends and acetal structures is involved in the propagation reaction with other Lewis acids such as ZrCl4. The trends in Lewis acids correlated with the nature of their central metals, i.e., their "oxophilicity" and "chlorophilicity".