Strong earthquakes pose significant risks to infrastructure because of liquefaction, a condition in which saturated earth becomes less rigid and strong. The purpose of this study is to determine whether Fly ash (FA) can reduce sand liquefaction. Cyclic triaxial strength tests are carried out in an undrained environment to recreate undrained field circumstances during an earthquake or other cyclical load for untreated sand specimens. These tests were conducted on sand specimens with varying FA content (0, 10, 20, and 30%) at a constant relative density of 30%. Additionally, monotonic shear tests were performed before and after liquefaction for sand samples at relative densities of 10, 20, and 30. Liquefaction resistance, quantified by the Cyclic Resistance Ratio (CRR), increased with both relative density and FA content. At 30% relative density, CRR values were 0.143, 0.146, 0.184, and 0.182 for 0%, 10%, 20%, and 30% FA, respectively. Monotonic shear tests revealed a substantial decrease in shear strength post-liquefaction for all samples. However, the residual strength exhibited a positive correlation with relative density. For instance, at 10%, 20%, and 30% relative densities, the maximum load decreased from 54.7 N, 107.3 N, and 254.4 N before liquefaction to 4.7 N, 10 N, and 14.7 N, respectively, after liquefaction. This research underscores FA’s effectiveness in enhancing sand's liquefaction resistance. The findings provide valuable insights for developing mitigation strategies to reduce the devastating impacts of liquefaction on built environments in earthquake-prone regions.