Polymeric solid electrolytes, with excellent cationic conductivity, were prepared from the complexation of lithium methoxyoligo(oxyethylene) sulfate and lithium methoxyoligo(oxyethylene) sulfonate with poly[methoxyoligo(oxyethylene)methacrylate-co-acrylamide]. The electrolytes exhibit low glass transition temperature and have almost no crystal. Their ionic conductivities at 25 degrees C are over 10(-5) S/cm. The carrier number in the complex decreases while ionic mobility increases considerably with increasing temperature. The polarization reversing method confirms that the cationic transference numbers are all over 0.9. The electrolytes have single ion conduction characteristics in DC polarization.