Ring opening polymerization of ethylene oxide by using coordination catalysts composed of neodymium 2-ethylhexyl phosphonates-triisobutyl aluminium-water in toluene have been studied. It was found that the catalytic activity of rare-earth coordination catalysts and visco--sity-average molecular weights of PEO obtained both are high. The kinetics for the polymerization of EO with Nd(P204)3 -Al(i-Bu)3-H2O system in toluene at 60℃ has been studied. The overall polymerization activation energy E. measured wat 33.8kJ/mol.and the rate equ-ation could be expressed as Rp=Kp[EO] [Nd(P204)3]