To develop highly conducting polymer electrolytes, dendritic polyether macromonomers were synthesized, and new network polymer electrolytes were prepared by photo-cross-linking reaction of the macromonomers with a dissolved lithium salt. The macromonomers were synthesized by the anionic ring-opening copolymerization of ethylene oxide (EO) and 2-(2-methoxyethoxy)ethyl glycidyl ether (MEEGE) in the presence of diglycerin as a starting material to yield dendritic polyether tetra-ol, followed by the partial methoxyethylation of the terminal hydroxyl groups and successive acrylation of the residual hydroxyl groups. Ionic conductivity of the polymer electrolytes was dependent on the molecular weight and the extent of methoxyethylation of the macromonomers and reached 10(-4) S cm(-1) at 30degreesC. The introduction of hyper-branched side chains into the network polymer electrolytes by using the dendritic macromonomers was effective for increasing the ionic conductivity.