The delignification of chemical pulps with laccase and N-hydroxybenzotriazole was explored employing a pre- and post-O-2 delignified softwood draft pulp. The delignification properties of laccase were shown to be improved with N-hydroxybenzotriazole was used as a mediator instead of 2,2＇-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid). Analysis of the structure of residual lignin before and after laccase/N-hydroxybenzotriazole treatment indicated that the biobleaching system oxidizes the phenolic component of lignin and that the residual lignin is demethylated and significantly enriched in carboxylic acid groups.