PURPOSE: To provide a manufacturing method of a polymer solid electrolyte having high ion conductivity and mechanical strength.

CONSTITUTION: A dispersing medium is removed from mixed dispersing liquid of high polarity polymer particulates and low polarity polymer particulates having crosslinking reactivity, and after a polymer matrix composed of a high polarity high polymer phase and a low polariry polymer phase is formed by coagulating and fusing the mutual polymer particulates, the high polarity high polymer phase is impregnated with an electrolyte. In a polymer matrix forming process, a polymer matrix precursor is soaked in a good solvent of the low polarity polymer phase, and the low polariry polymer phase is heated and crosslinked. Or in a heat treatment process in the high polymer matrix forming process, heat treatment is performed at a temperature less than and not less than a crosslinking reaction temperature of a low polariry polymer.