Abstract: The environmental impact of traditional cement-based materials has led to the growing interest in sustainable alternatives like geopolymer concrete. Geopolymers formed from the alkali activation of alumino-silicate materials like metakaolin have lower carbon emissions and promising mechanical properties. However, their brittleness and moisture sensitivity limit their wider use in structural applications. Natural fibers due to their biodegradability and cost effectiveness have emerged as viable reinforcement but their hydrophilic nature can negatively impact durability unless properly treated. This study investigates the comparative effect of untreated, water-retted and alkali treated plantain fibers on the water absorption, dimensional stability and compressive strength of metakaolin based geopolymer concrete. Experimental results showed that alkali treated fibers gave the best results with lowest water absorption (6.88%), minimal thickness swelling (2.82%) and highest average compressive strength (11.6 MPa). Untreated fibers had poor moisture resistance and moderate strength while water retted fibers had better dimensional behavior but lower mechanical properties. Microstructural analysis using SEM and FTIR confirmed better fiber matrix bonding in alkali treated samples, hence the role of surface modification in improving material properties. The findings show that proper treatment of natural fibers improves both structural and durability properties of geopolymer concrete, a pathway to greener construction. The study recommends alkali treatment for load bearing applications and further research on hybrid treatments and other agricultural fibers for wider regional applicability.