This study investigates the potential of Ficus Macrocarpa tree bark fibers (FMB) as a sustainable alternative reinforcement for polymer composites. The fibers were extracted from FMB and subjected to alkali treatment to evaluate their impact on physical, chemical, and thermal properties. The initial fiber diameter was 253.80 ± 15 μm, which reduced to 223.27 ± 12 μm after treatment. Chemical analysis showed an increase in cellulose content to 59.7 wt%, a 23.34% improvement over untreated fibers (48.4 wt%). The crystalline index for treated and untreated fibers was 84.75% and 80.20%, respectively, with no noticeable changes in the cellulose phase. The crystalline size increased to 3.21 nm. Thermogravimetric analysis demonstrated enhanced stability up to 378.87 °C, while the kinetic activation energy remained constant at 64.76 kJ/mol for both types of fibers. The alkali treatment also improved surface roughness to 39.26, confirmed by scanning electron microscopic images. These findings highlight the potential of FMB fibers as a sustainable and environmentally friendly replacement for synthetic fibers in polymer composites, offering enhanced physical properties and excellent thermal stability.This study investigates the potential of Ficus Macrocarpa tree bark fibers (FMB) as a sustainable alternative reinforcement for polymer composites. The fibers were extracted from FMB and subjected to alkali treatment to evaluate their impact on physical, chemical, and thermal properties. The initial fiber diameter was 253.80 ± 15 μm, which reduced to 223.27 ± 12 μm after treatment. Chemical analysis showed an increase in cellulose content to 59.7 wt%, a 23.34% improvement over untreated fibers (48.4 wt%). The crystalline index for treated and untreated fibers was 84.75% and 80.20%, respectively, with no noticeable changes in the cellulose phase. The crystalline size increased to 3.21 nm. Thermogravimetric analysis demonstrated enhanced stability up to 378.87 °C, while the kinetic activation energy remained constant at 64.76 kJ/mol for both types of fibers. The alkali treatment also improved surface roughness to 39.26, confirmed by scanning electron microscopic images. These findings highlight the potential of FMB fibers as a sustainable and environmentally friendly replacement for synthetic fibers in polymer composites, offering enhanced physical properties and excellent thermal stability.