The present invention relates to a process for producing a polymer structure comprising: mixing and unifying a matrix polymer made of a linear polymer and a highly-branched polymer having hydrophilic functional groups at molecular ends and to form a structure containing the matrix polymer and the highly-branched polymer; and subjecting the obtained structure to either immersion in water and/or a hydrophilic solvent or exposure to an atmosphere of vapor of water and/or a hydrophilic solvent at a temperature ranging from a temperature lower than Tg of the matrix polymer by 30° C. to decomposition temperature of the matrix polymer; wherein the hydrophilic functional groups at the molecular ends of the highly-branched polymer are distributed in outermost surface of the polymer structure at an enhanced density. The present invention also relates to a process for producing a polymer structure in which vinyl polymer chains are grafted to at least a part of the hydrophilic functional groups.