The present invention relates to a method for preparing an end site-specific macromolecule-bile acid oligomer conjugate, comprising conjugating a bile acid oligomer which is prepared by oligomerization of two or more bile acid monomers to the terminal site of a macromolecule; a method for body absorption of an end site-specific macromolecule-bile acid oligomer conjugate, comprising administering the macromolecule-bile acid oligomer conjugate prepared by the above method to a subject orally; an end site-specific macromolecule-bile acid oligomer conjugate wherein the bile acid oligomer is conjugated to the terminal site of macromolecule; a composition comprising the conjugate; an oral formulation for macromolecule comprising the conjugate, a solubilizer, an excipient, a disintegrant, a binder, and a lubricant; a pharmaceutical composition comprising a heparin-bile acid oligomer conjugate wherein the bile acid oligomer is conjugated to the terminal site of heparin; and a method for treating thrombosis using said composition.