Cellulose is an interesting biopolymer due to its employment in many motivating applications such as composites, pharmacy, textiles, decolorization, etc. The current work describes the extraction of fibrillated cellulose from Forsskaolea tenacissima leaves using alkalization and bleaching processes. The techniques of SEM, XRD, FT-IR, and TGA-DTA were used to analyze the untreated substrates and the extracted fibrillated cellulose. FT-IR data indicated that, after alkalization and bleaching processes, lignin and hemicellulose initially present in untreated leaves, were removed. The crystallinity index [CrI (%)] values calculated for extracted fibrillated cellulose and Forsskaolea tenacissima leaves were equal to 42.85% and 23.2%, respectively. The high CrI value calculated for the extracted fibers demonstrated the removal of the amorphous components in untreated leaves. TGA analysis showed that alkalization and bleaching processes affected the thermal events. At equilibrium, the adsorption capacities of bleached fibers were 220 mg/g and 185 mg/g for methylene blue (MB) and crystal violet (CV), respectively. The adsorption process was exothermic and non-spontaneous. Overall, the adsorption results confirmed that the extracted fibers could be used as effective adsorbents of cationic dyes from water