Abstract: Two laccase-mediator systems（LMSA and LMSB） respectively consisted of laccase（EC1．10．3．2） A as well as laccase B and their mediator of1-hydroxybenzotriazole（HBT） were used to biobleach reed kraft pulp which was then extracted with soda．Kappa number and viscosity of the bleached pulps were determined．The results confirm that the LMS biobleaching exhibits excellent delignification selectivity．Higher level of delignification was obtained in LMSB stage than in LMSA stage．UV-Vis absorption spectra of laccases A and B reveal that laccase B contains less aromatic amino acid residues than laccase A does‚which makes laccase B less vulnerable to HBT·attack．So the reaction between HBT·and the residual lignin in LMSB biobleaching becomes easier．This is the reason for the more excellent delignification efficiency of LMSB compared to LMSA． 

Key words: laccase-mediator system, reed kraft pulp, delignification, biobleaching