Modulation-doped ZnO multi-layer structures were synthesized and their electrical properties were investigated. First, Al_xMg_yZn_l-x-yO films were prepared as carrier injection layers for modulation doping. The films were deposited on sapphire (1120) substrates by pulsed laser deposition using Nd : YAG laser with the wavelength of 266 nm. It is confirmed that the modification of a band gap and heavy electron doping can be simultaneously achieved in the films. Secondly, modulation-doped multi layer [ZnO/Al_0.01Mg_0.05Zn_0.94O]₁₀ was grown on a sapphire (1120) subatrate. X-ray diffraction pattern of the film showed the satellite peaks corresponding to the multi-layer period. Hall mobility of the film was 43 cm²/V⋅n, which was close to that of Al^xMg^yZn^l-x-yO single-layer.