Modified polymers containing a poly(2-hydroxyethyl(meth)acrylate) chain as the hydrophilic polymer segment in which a hydrophobic polymer chain or a lipid residue of a sterol is bound to either end of the poly(2-hydroxyethyl(meth)acrylate) chain through a covalent bond or in which the poly(2-hydroxyethyl(meth)acrylate) chain is grafted onto the backbone chain at either end thereof. These modified polymers are excellent in compatibility with liquid or a living body, thus being advantageously usable particularly in medical fields.