The ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC) initiated with highly active single rare earth tris(2,6-di-tert-butyl-4-methylphenolate) (Ln(OAr)3, Ln=La, Nd, Dy, Y) is reported for the first time. The catalytic activities of various Ln(OAr)3 systems are decreasing in the following sequence: La>Nd>Dy～Y. PolyDTC (Mw=17.1×104, MWD=2.79) initiated by La(OAr)3 at [DTC]/[initiator]=1000 was obtained with a conversion of 97.9% within 1 h in toluene at 15℃. 1H NMR, GPC, and DSC are used to characterize the polymer's structure and to investigate the polymerization mechanism. PolyDTC obtained has no ether unit developed from CO2 elimination. The polymerization of DTC occurs according to a coordination anionic mechanism, and the ring is opened via acyl-oxygen cleavage leading to an Ln-O active center.