<p>This work reports some experimental data on lignins extracted from Algerian olive husk flour using two distinct methods, i.e., alkaline and ethanol organosolv. The objective was to compare the structural and thermal properties of alkaline lignin (ALK) and organosolv lignin (EOL) by several techniques, i.e., attenuated total reflectance Fourier transform infrared spectroscopy, carbon-13 and proton nuclear magnetic resonance (¹³C NMR and ¹H NMR), ultraviolet spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. The effect of each extraction method on the antioxidant activity of lignin was assessed based up on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The study showed that the chemical structure of the lignin was not affected whatever the extraction method. Indeed, NMR analysis indicated that both ALK and EOL were primarily composed of syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units, with depolymerization mainly occurring via β-O-4 linkages. However, the organosolv method resulted in a higher yield of lignin with higher purity and a smaller particle size compared to the alkaline method. As expected, XRD analysis showed the amorphous nature of both ALK and EOL, indicating the absence of long-range crystalline order. Thermal analysis indicated that ALK exhibited a lower thermal stability than EOL, due to the presence of carbohydrate residues in its structure. Whereas, a higher antioxidant activity was observed with EOL compared to ALK. The results highlight the effectiveness of ethanol organosolv method over the alkaline one for lignin extraction by providing a better suitable material for engineering and high-value applications.</p> Graphical Abstract <p></p>