The accelerating and increasing pace of urban development and the surge in construction activities have resulted in a substantial increase in demolition waste, like concrete waste. Re-using the same materials for a new construction application can give a sustainable strategy to reduce environmental impact and conserve limited natural resources. This study shows the possible advantages of using recycled fine aggregate (RCA) as a partial instead of natural aggregate in cement mortar. RCA which is incorporated in cement mortar mixtures at different varying percentages (0%, 5%, 10%, 15%, 20%, and 25%) and compressive strength tests are done for curing ages of 7 days and 28 days. The results of RCA replacing on the mechanical performance of mortar, identifying the optimal percentage for strength enhancement. Furthermore, field emission scanning electron microscopy (FESEM) analyzation was performed on the 28-day mortar samples with the highest compressive strength for each replacement level to examine microstructural characteristics. The study has significant and valuable results in the field of recycled concrete and sustainable construction provided a potential alternative to traditional aggregates