Fly ash and ground bottom ash are suitable source materials for producing geopolymers. The results of the FT-IR, DSC thermogram, SEM, and XRD analyses indicate that fly ash is more reactive than bottom ash and gives a higher degree of geopolymerization. The compressive strength of the fly ash geopolymer mortar is reasonably high at 35 MPa, and it is significantly higher than the 18 MPa of the bottom ash geopolymer mortar. The strength of a geopolymer is also dependent on NaOH concentration. The optimum NaOH concentration of 10 M is suitable for both ash materials.