A solid polymer electrolyte, a lithium battery employing the same, and methods of forming the electrolyte and the lithium battery. The polymer electrolyte includes polyester (meth)acrylate having a polyester polyol moiety having three or more hydroxide (—OH) groups, at least one hydroxde group being substituted by a (meth)acrylic ester group and at least one hydroxide group being substituted by a radical non-reactive group, or its polymer, a peroxide having 6 to 40 carbon atoms, and an electrolytic solution including a lithium salt and an organic solvent.