Nylon 6 (Ny6) composites reinforced with treated agave fiber (AF) at different concentrations (5–20 wt%) were achieved by melt mixing process at 250°C, without the addition of any compatibilizing or coupling agents, and characterized in terms of their structural, morphological, and mechanical properties. The alkaline‐ultrasound (NaOH‐U) treatment in AF resulted in the removal of the low thermal stability components (pectin and hemicellulose), concentrating the cellulose fraction, and favoring the crystallinity percentages (Xc) of the Ny/AF composites. Moreover, the interfacial interactions between functional groups of agave fiber and Ny6 resulted in the increase Young's modulus (18.8%), flexural strength (11.3%), and density (3.7%). These findings could be useful when looking for potential applications in the mobility industry.