The present invention presents a solid polymer electrolyte consisting of a multiphase polymer matrix and an electrolyte solution. The polymer matrix consists of a highly polar polymeric (HPP) phase impregnated with the electrolyte solution to form ion conducting channels, and a less polar polymeric (LPP) phase, constituting the support structure. Further, the invented solid polymer electrolyte may also include a second ion conducting channels, forming a multiphase microstructure in which the electrolyte solution is present around the LPP particles as a fine mesh-like network. The invention also presents two kinds of method for making such a solid polymer electrolyte. The first includes the steps of: making a multiphase polymer matrix; and impregnating the polymer matrix with an electrolyte solution. The second includes the steps of: making a multiphase polymer matrix containing an electrolyte in advance; and impregnating the multiphase polymer matrix containing the electrolyte with a solvent to dissolve the electrolyte or electrolyte solution in the polymer matrix.