A composition for a gel polymer electrolyte, the composition comprising a lithium salt, a non-aqueous organic solvent, a polymerization initiator, and an oligomer, wherein the oligomer comprises at least one selected from the group consisting of oligomers represented by Formula 1: wherein, in Formula 1, R' and R" are each independently an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R 1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, -CO-OR- (where R is an alkylene group having 1 to 10 carbon atoms), -R o -CO- (where R o is an alkylene group having 1 to 10 carbon atoms), or -R i -O-R' i - (where R i and R' i are each independently a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms), R 2 is -R 4 -CO-O-, where R 4 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, or a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, R a , R b , R c , and R d are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, n and m are the numbers of repeating units, wherein n is an integer of 1 to 100, and m is an integer of 1 to 100, a and c are each independently an integer of 0 to 2, and b and d are each independently an integer of 1 to 3. wherein the oligomer comprises at least one selected from the group consisting of oligomers represented by Formula 1: wherein, in Formula 1, R' and R" are each independently an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R 1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, -CO-OR- (where R is an alkylene group having 1 to 10 carbon atoms), -R o -CO- (where R o is an alkylene group having 1 to 10 carbon atoms), or -R i -O-R' i - (where R i and R' i are each independently a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms), R 2 is -R 4 -CO-O-, where R 4 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, or a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, R a , R b , R c , and R d are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, n and m are the numbers of repeating units, wherein n is an integer of 1 to 100, and m is an integer of 1 to 100, a and c are each independently an integer of 0 to 2, and b and d are each independently an integer of 1 to 3. <EOS>