 This study investigates the feasibility of using alkaline activation and treated coir fibers to improve the engineering characteristics of soils and subgrade performance of pavements by adding fly ash precursor and physically treating fiber surface with linseed oil. The results show that the addition of alkali-activated fly ash and inclusion of treated fibers led to increasing deformability and failure strain, resulting in a denser and more uniform structure. The findings encouraged the application of a stabilized soils reinforced with treated fibers to improve the strength of soils in alkaline environment as subgrade of pavements. This article was authored by Tang Tang Tan, Bu Jiang Bi Ke Huot, Vivian Grainy and others.