Typically, for production of high brightness pulp, the residual lignin in unbleached kraft pulp is commonly removed through a multi-stage bleaching process with the use of chlorine species. The effluent from such a bleaching process is dark brown due to their content of chromophoric and polymeric lignin derivaties. Moreover, the organically bound chlorine [measured as total organically bound chlorine (TOCI) or adsorbable organic halogen (AOX)] is present in a wide range of organic materials which have toxic and mutagenic properties. It has recently been discovered that small quantities of dioxines [polychlorinated dibenzo dioxin (PCDD) and polychlorinated dibenzo furan (PCDF)] can also appear in bleach plant effluents. Consequently, this bleaching effluent is not easily recycled within a mill recovery system because of the potential corrosion problems created by its high chlorine content and finally affects the harmful effects on the environment. The purpose of the present research is to describe the decolorization of the E_1 effluent with white-rot fungi showing the ligninolytic activity, to accomplish efficient treatment of kraft bleachery efficient with less energy and in relatively short treatment-period. First, it was attempted to design the effective treatment process of the E_1 effluent with the fungus IZU-154 showing ligninolytic activity. It has revealed that the color of the effluent was effectively removed when glucose was added as an additive. Furthermore, the addition of glucono-$ delta $-lactone to the E_1 effluent produced a more remarkable degree of decolorization than did that of glucose. All white-rot fungi tested showed high decolorization effect of the E_1 effluent in the presence of glucono-$ delta $-lactone. It is suggested that the effect of glucono-$ delta $-lactone on the high decolorization of E_1 effluent are closely associated with the activity of the surfaces of the mycelium due to the change of pH of the effluent during fungal treatment. Moreover, to establish a more practical system for the decolorization of the bleaching effluent, a screening have been performed to find fungi having high decolorization activity of the E_1 effluent without any additional nutrients. The strains which had the activity of decolorization were isolated from 1,212 samples of rotted wood of forest habitats. Among the isolated fungi, the fungus KS-62 showed the most effective decolorization of the E_1 effluent and degraded the chlorinated lignin in the E_1 effluent without any additional nutrients. Moreover, the treatment with KS-62 significantly reduced the COD and AOX and decreased the high molecular weight of chlorolignins in the E_1 effluent. To obtain a reasonable basis for the evaluation of an industrial fungal treatment, we have performed the treatment of the E_1 effluent with the immobilized mycelium of the fungus KS-62. The fungal biomass of KS-62 could be maintained for a long-term (at least 40 days) without any appreciable loss of activity in the presence of a critical amount (between 0.050% and 0.075%) of glucose. The COD of the E_1 effluent treated with KS-62 was lower than that of initial E_1 effluent in whole treatment period, which indicated that the fungus KS-62 decomposed the chlorolignin in the E_1 effluent. Based on these experiments, it has become apparent that the biological decolorization of bleaching effluents has been enabled with the lignin-degrading fungi.