It has been claimed that heat treatment is necessary for the reaction of geopolymer to achieve the desired strength and form. However, it’s also the drawback affecting the application of Geopolymer in the construction site. There-fore, instead of heat treatment, the other important factors for synthesizing the geopolymer matrix in the soft soil environment, is the main focusing of this paper. The Taguchi method was used to determine the most important factor that affects several properties of geopolymer modified sludge by minimizing the effects of variation, but without eliminating the cause. The results indicate that the geopolymer content, clay content in sludge, initial water content and moisture content play a unique role in different properties of modified sludge.