This study investigates the alkali-silica reactivity (ASR) in fly ash-based geo-polymer concrete using silica fume as a partial replacement under varied molarity conditions. ASR is a known issue in concrete, especially in hydraulic structures, due to the interaction between alkalis in cement and reactive aggregates in the presence of moisture, resulting in structural degradation. Geo-polymer concrete, an innovative material produced from the polymerization of inorganic compounds like fly ash and alkali solutions, presents a sustainable alternative to Portland cement. The study uses accelerated ASR testing on geo-polymer concrete specimens with varying molarities and silica fume replacements to assess resistance against ASR expansion. Results demonstrate improved ASR resistance in specimens with higher molarity and increased silica fume content, offering potential benefits for mass concrete applications in moisture-prone environments. This study suggests a specific mix ratio as optimal for ASR control, providing a viable option for sustainable construction.