ZnO/Mg0.1Zn0.9O multiquantum-well (MQW) structures were grown on ZnO substrates by molecular beam epitaxy. Abrupt interfaces and well/barrier width in the MQWs were confirmed by x-ray diffraction measurement and transmission electron microscopy. The transition energy of the localized exciton in the ZnO/Mg0.1Zn0.9O MQWs with well/barrier width of 5/8 nm was found to be about 3.375 eV at low temperature, consistent with theoretical calculation. The first subband energies in the conduction and valence band were calculated to be 19.2 and 5.4 meV, respectively. The transition energy showed no shift with excitation power, indicating that the polarization-induced electric field is negligible in the ZnO/Mg0.1Zn0.9O MQW structures.