Pine and wheat straw alkali lignin (PAL and WAL) were sulfomethylated to improve water solubility, polymerized with horseradish peroxidase (HRP) to improve the molecular weight (M-w) and applied to dope and disperse polyaniline (PANI). The structural effect of lignin from different origins on the reactivities of sulfomethylation and HRP polymerization was investigated. The results show that WAL with less methoxyl groups and lower M-w have higher reactivity in sulfomethylation (SWAL). More phenolic hydroxyl groups and lower M-w benefit the HRP polymerization of sulfomethylated PAL (SPAL). Due to the natural three-dimensional aromatic structure and introduced sulfonic groups, SPAL and SWAL could effectively dope and disperse PANI in water by pi-pi stacking and electrostatic interaction. HRP modified SPAL (HRP-SPAL) with much higher sulfonation degree and larger M-w significantly increased the conductivity and dispersibility of lignin/PANI composites. (C) 2017 Published by Elsevier B.V.