Lignin is the second largest naturally renewable resource and is primarily a by-product of the pulp and paper industry; however, its inefficient use presents a challenge. In this work, Fe₃O₄ nanoparticles loaded on lignin nanoparticles (Fe₃O₄@LNPs) were prepared by the self-assembly method and it possessed an enhanced peroxidase-like activity. Fe₃O₄@LNPs catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a blue color, was observable by the naked eye. Under the optimal conditions, Fe₃O₄@LNPs showed the ability of sensitive colorimetric detection of H₂O₂within a range of 5–100 μM and the limit of detection was 2 μM. The high catalytic activity of Fe₃O₄@LNPs allows its prospective use in a wide variety of applications, including clinical diagnosis, food safety, and environmental monitoring.