For the value-added utilization of industrial lignin both from pulping black liquor and acid hydrolysis residues, the eucalyptus alkali lignin (AL) and enzymatic mild acidolysis corncob-to-xylitol residue lignin (EMARL) were isolated. Their pyrolysis behaviors were investigated by thermogravimetric analysis (TGA), in situ Fourier transform infrared spectroscopy (FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The chemical bonds of EMARL were easier to break than AL at relatively lower temperatures, which was confirmed by the relationship between temperature and the differential absorbance of functional groups (such as carbonyl and hydroxyl). Based on the analysis of pyrolysis products, the value-added monomers were the main products. At 400 °C, AL mainly contained guaiacyl-type and syringyl-type compounds and the yields were 28.95% and 62.54%, respectively, while EMARL contained more guaiacyl-type products (62.96%). When the temperature was increased to 600 °C, the contents of phenol-type increased, suggesting that the demethoxylation reaction occurred during lignin pyrolysis. Study of the characteristics of pyrolysis could be significant for understanding the thermochemical depolymerization of AL and EMARL for value-added products.