Low ionic conductivity is one of the issues for polymer electrolytes to be used in commercial batteries, though they have been viewed as the promising electrolytes in all-solid lithium-ion batteries for several decades. Here, we show an enhanced ionic conductivity in a classic polymer electrolyte by controlling the ionic conductive pathway via a core–shell structure. The enhancement in ionic conductivity is contributed from the formation of a controlled 3D network of the ion conductive amorphous phase. The result suggests that the core–shell structure design can realize the control of the conduction pathway, which is significant for understanding the ionic conductive behaviors as well as for the improvement of the ionic conductivity in polymer electrolytes.