Ring-opening polymerization of ε-caprolactone catalyzed by rare earth chloride dissolved in N,N-dimethylformamide and adding a small amount of propylene oxide was studied.The optimum conditions for the ring-opening polymerization of CL are as follows.In the bulk polymerization: n（DMF）/n（LaCl3）=10,n（PO）/n（LaCl3）=20,aging temperature: 30 ℃,aging time: 1 h,c（CL）=7.91×10-3 mol/L,c（LaCl3）=1.58×10-5 mol/L,the polymerization carried out at 30 ℃ for 1 h,yield=83.3%,Mν=1.93×104.In the solution polymerization: n（DMF）/n（LaCl3）=10,n（PO）/n（LaCl3）=20,aging temperature: 30 ℃,aging time: 1 h,toluene as the solvent,c（CL）=4.22×10-3 mol/L,c（LaCl3）=8.43×10-6 mol/L,the polymerization was carried out at 30 ℃ for 2 h,yield=62.9%,Mν=1.21×104.
