A novel core-shell type branched macromolecule was synthesized from the tris(hydroxymethyl) aminomethane(Tris) and the monomethoxypoly(ethylene glycol)(mPEG). The first step was to protect the amino group of Tris by using t-butyloxycarbonyl anhydride ((Boc)2O), then mPEG was activated by changing hydroxide terminal into acid chloride and carboxylation of mPEG was fulfilled before. The amino group was reserved so that it could be used as functional radical to modify the protein later. The product was confirmed to inosculate with FT-IR, EA and M.W. through infrared spectroscopic analysis, element analysis and mensuration of molecular weight.