A multiblock copoly(ester-ether) consisting of poly(L-lactic acid) (PLLA) and poly(oxypropylene-co-oxyethylene) (PN) was prepared and characterized. Preparation was done via the solution polycondensation of a thermal oligocondensate of L-lactic acid, a commercially available telechelic polyether (PN: Pluronic-F68), and dodecanedioic acid as a carboxyl/hydroxyl adjusting agent. When stannous oxide was used as the catalyst, the molecular weight of the resultant PLLA/PN block copolymers became very high (even with a high PN content) under optimized reaction conditions. The refluxing of diphenyl ether (solvent) at reduced pressure allowed the efficient removal of the condensed water from the reaction system and the feed-back of the intermediately formed L-lactide at the same time in order to successfully bring about a high degree of condensation. The copolymer films obtained by solution casting became more flexible with the increasing PN content as soft segments.