The present work demonstrates the function of multi-branched poly(L-lactide) based on polyethylenimine cores (mPEI-PLLA) as an additive to drastically enhance the elongation of PLA resin. By simply applying mPEI as the core molecule with a catalytic amount of tin octoate, LLA ring-opening polymerization is accomplished to result in multi-branched PLLA, i.e. mPEI-PLLA. The blend of mPEIPLLA with PLA in the film form represents the significant increase of elongation at break for as high as 280% without significant changes in Tg, indicating the role of branching PLLA to induce amorphous phase in the packing structure of PLA. The ease of mPEI-PLLA preparation and the superb elongation at break provided to PLA convince us that mPEI-PLLA is a practical miscible additive to solve the brittleness of PLA. (C) 2016 Elsevier Ltd. All rights reserved.