This research investigates the influence of the fineness of lowcalcium fly ash on the compressive strength of geopolymer concrete. Fly ash was procured from two different thermal power plants and subjected to grinding in a Los Angeles Abrasion Testing Machine for 250 and 500 revolutions to achieve finer particle sizes. Geopolymer concrete was synthesized by activating these fly ashes with a 14M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution mixed in the ratio of 1:2.5, respectively, to produce the alkaline activator solution. The activated fly ash was then combined with fine and coarse aggregates and water to form the concrete mix. Specimens were heat-cured at 80°C for 24 hours to enhance geopolymerization. Compressive strength tests revealed that increased fly ash fineness led to a significant enhancement in strength, with improvements of approximately 7 % for chabra low calcium fly ash (CLCF)-based concrete and 9 % for kota low caclium fly ash (KLCF)-based concrete. These findings highlight the importance of fly ash fineness in enhancing geopolymer concrete’s mechanical properties, confirming its potential for sustainable construction Future research could explore the impact of varied curing conditions, different fly ash sources, and long-term durability tests to further enhance the understanding and applicability of geopolymer concrete.