Ring-opening polymerization (ROP) of various oxirane derivatives of the type, 2,2-R-1,R-2-CCH2O [R-1 = H (1), CH3 (2); R-2 = CH3 (a), CH2Cl (b), CH2OCH3 (c)], using organotin phosphate (Bu2SnO-Bu3PO4) condensate has been explored. The ROP of monosubstituted oxiranes (1a-c) afforded ring-opened polymers in high yields (1a, 1c = 99% and 1b = 69%); the resultant polymers from monomers 1a and 1b possessed high molecular weights (M-n = 9.49 x 10(4), 10.60 x 10(4), respectively). In contrast, both polymer yields and molecular weights for resultant polymers in the polymerization of disubstituted oxiranes (2a-c) were considerably lower than those in the polymerization of monosubstituted monomers (1a-c). ROP of glycidyl 2-methylglycidyl ether (3) possessing two oxirane groups with different reactivity was thus conducted by organotin catalyst; the high molecular weight polyether (M-n = 9.17 x 10(4)) containing oxirane ring in the side chain has successfully been obtained in moderate yield.