 The relationship between cellulose crystallinity, extractive content, and lignocellulosic fiber degradation was investigated using FTIR spectroscopy, X-ray diffraction, and thermogravimetry techniques, revealing that higher extractive contents lead to lower crystallinity and smaller crystallite size, accelerating the degradation process and reducing thermal stability. Additionally, increasing cellulose crystallinity and crystallite size shifts the thermal decomposition temperature of natural fibers. This study provides valuable information about the structure and properties of lignocellulosic fibers for composite formulations. This article was authored by Mateus Paletto, A. Torrell, and Ademir Jayzadara.