Currently, a soil stabilization approach using fly ash as an effective choice for increasing soil stiffness and strength has emerged. With the presence of water, the lime in the fly ash would be separated, generating cementitious materials binding the grains of sand. In the present study, the influence of curing time and saturation during specimen preparation on the behavior of fly ash-rectified loose-grained sand was observed by performing a series of splitting tensile strength tests. It was found that the splitting tensile strength increases with fly ash content and curing time and decreases with porosity and saturation. The increase in splitting tensile strength due to the reduction in saturation was clarified using microscopic image observations. Fly ash bonds congregate at the contact surface between the grains of sand at a low saturation of 30% and spread evenly on the whole sand surface at a high saturation of 100%. The splitting tensile strength produced at 30% saturation was approximately twofold higher than that at 100% saturation, particularly at one month of curing time. However, the splitting tensile strength at higher saturations approaches that at lower saturations, especially at longer curing times. Porewater evaporation accelerates the self-hardening occurring over time during curing, helping to achieve optimal strength. A reduction in porosity of approximately 0.6% caused by adding fly ash to the mixture can increase the splitting tensile strength by up to twenty-fold in the present study. An equation has been proposed as a function of porosity/volumetric fly ash content, curing time, and saturation during the preparation of the specimen. That equation can be applied convincingly to determine the splitting tensile strength of fly ash-rectified sand.