The present invention provides a polymer solid electrolyte excellent in thermal properties, physical properties and ion conductivity and being close to practical level; especially, a totally solid electrolyte and a composition for producing the same. A composition for polymer solid electrolyte includes a copolymer having repeating units represented by Formula (I): (wherein each of R1 to R3 independently represents a hydrogen atom or a C1-C10 hydrocarbon group; R4a and R4b independently represents a hydrogen atom or a methyl group; R5 represents a hydrogen atom, a hydrocarbon group, an acyl group or a silyl group; and m is an integer of 1 to 100), and repeating units represented by Formula (II): (wherein each of R6 and R8 independently represents a hydrogen atom or a C1-C10 hydrocarbon group; R9 represents an organic group having at lease one functional group selected from the group consisting of hydroxyl group, carboxyl group, epoxy group, acid anhydride group and amino group); and an electrolyte salt.