In this research, the geopolymer was fabricated using municipal solid waste incineration ash (denoted as MSWIA)slag and alkali activator, NaOH and its properties were analyzed. Particularly, the effects of NaOH molarity, particle size ofMSWIA, and liquid/solids ratio on the compressive strength of geopolymers were investigated. The compressive strength ofgeopolymers fabricated increased with finer grain size of MSWIA, and optimum value of the liquid/solids ratio wasidentified as 0.13. As the molarity of the NaOH increased, the compressive strength of geopolymers was increased. Evenmore the 20 M of NaOH, but the strength was not increased. The calcium aluminum silicate and calcium aluminum silicatehydrate zeolites were generated in the geopolymer fabricated with more than 20 M of NaOH, with some unreacted silica andunknown crystals remained. The highest compressive strength, 163 MPa, of geopolymer was appeared at conditions of curingtemperature 70oC, and 20 M of NaOH, indicating that the high concentration of NaOH accelerates the geopolymer reactionand dense microstructure. The high-strength geopolymer fabricated in the present study is expected to contribute significantlyto develop the field of cement alternative substances and to improve the recycling rate of MSWIA slag.