This study examines the impact of ultrafine fly ash (UFFA) as a partial replacement for cement in self-compacting concrete (SCC), with replacement levels ranging from 0% to 20%. UFFA is derived by refining conventional fly ash into finer particles, which enhances its pozzolanic reactivity, improves packing density, and reduces porosity. The research focuses on how this modification influences fresh properties, including flowability, passing ability, and resistance to segregation, ensuring the mix remains highly workable without external compaction. Along with fresh properties, early compressive strength at 7 days is evaluated to determine whether UFFA impacts strength development while maintaining the self-compacting nature of the mix. Since SCC is widely used in structural applications that demand both high fluidity and durability, optimizing the level of UFFA is essential for achieving a balance between workability and mechanical strength. Beyond performance improvements, this study highlights the environmental advantages of using UFFA, as it helps reduce cement consumption and repurpose industrial by-products, making concrete production more sustainable. The findings from this research will provide practical insights into the ideal UFFA replacement percentage, helping to develop SCC mixes that are not only strong and efficient but also aligned with the construction industry’s shift toward greener and more durable materials.