This study aims to elucidate the effect of LPSO phases on the corrosion behavior of magnesium alloys through experimental design. The microstructure and corrosion behavior of four Mg-Zn-Y alloys designed according to the minimum structural unit for forming the 18R-LPSO phase, i.e. Zn/Y=3/4 (molar ratio), were studied in a comparative manner. The results showed that the alloys mainly contained α-Mg and 18R-LPSO phases, and the volume fraction of the 18R-LPSO phase increased with the increase of Zn and Y contents. The volume fraction of the 18R-LPSO phase in the four alloys was, in sequence, 16.55%, 34.45%, 54.24% and 70.36%, and the spatial distribution of the 18R-LPSO phase also changed from discrete blocks to continuous networks. When the volume fraction was about 50%, the corrosion resistance of the alloy was the best. When the volume fraction was greater than or less than 50%, the corrosion resistance of the alloy decreased.