Flexible and conductive polypyrrole (PPy) paper shows the potential use in electromagnetic shielding, antistatic packaging, and electrochemical materials due to its low cost and facile manufacturing procedure. However, the poor mechanical strength and relatively low electrical stability of PPy paper is still challenging. In this study, we use horseradish peroxidase polymerized sulfonated alkaline lignin (HSAL) as a dispersant and dopant for PPy and demonstrate mechanically strong and electrically stable PPy paper by a combination of multiple impregnations and in-situ polymerization. The abundant sulfonic, carboxyl, and phenolic hydroxyl groups of HSAL could significantly improve the interfacial interaction between cellulose fibers and PPy. Meanwhile, its high molecular weight facilitated the uniform distribution of pyrrole along the fiber axial direction during in-situ polymerization. As a result, the resulting PPy paper exhibits enhanced mechanical properties and electrical stability, as well as high conductivity (24.84 S cm(-1)). More significantly, we investigated the influences of the dosage of HSAL and the cycles of multilayer impregnations on the electrical and mechanical properties of PPy paper. This work sheds light on the design and fabrication of flexible and conductive PPy paper with superior mechanical robustness and stable electrical performance. (C) 2019 Elsevier Inc. All rights reserved.