Biobased and environmental-friendly polylactones provide a solution to the increasing crisis of fossilsourced products. Ring-opening polymerization (ROP) of ε-decalactone (DL) catalyzed by lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) [La(OAr) 3 ] and lanthanum tris-(borohydride) [La(BH 4 ) 3 (THF) 3 ] is reported for the first time in this paper. Both of them exhibit good activities producing poly(ε-decalactone) (PDL) with molecular weight (MW) up to 26.4 kg/mol and polydispersity index (PDI) as low as 1.10. PLLA-b-PDL-b-PEG-b-PDL-b-PLLA pentablock copolymers with predictable MWs and relatively narrow PDIs (1.19−1.28) are synthesized by sequential ROP of DL and Llactide (LLA) catalyzed by La(OAr) 3 in the presence of poly(ethylene glycol) (PEG). Chain extension reactions of the obtained pentablock copolymers are carried out using L-lysine diisocyanate (LDI) to produce multiblock copolymers with relatively high MW. The thermal behaviors studied by DSC and DMA measurements indicate that PDL is completely amorphous under ambient temperature and the copolymers with two T g s suggest microphase separation of hard and soft domains. We employ tensile tests to assess mechanical properties and find excellent elongation up to 723% of the chain-extended samples. Considering the biorenewable resource of DL and LLA, a novel, biobased, biodegradable, and biocompatible elastomer is successfully synthesized.