This study investigates the structural properties of Rice Husk Ash (RHA) and its potential as a cement substitute. Cement was gradually replaced with RHA (from 0% to 25% in 5% increments) to assess its effects on the mechanical and physical attributes of cement mortar, including microstructure analysis. Tests were conducted on samples cured for 3, 7, and 28 days. It was observed that replacing more than 10% of cement with RHA resulted in a dry mix, hindering proper hydration and leading to decreased strength. Additionally, the consistency of cement increased as the percentage of RHA increased, with the compressive strength peaking at 15% RHA. XRD analysis revealed the presence of quartzite and coesite minerals in RHA, indicating high silica content. Thermal analysis showed weight loss of RHA, and phase transition was examined between 600 and 1000°C using DSC. Microstructure analysis using SEM and EDS was conducted on cured cement mortar with RHA at different intervals.