Wastewater containing kraft lignin (KL) discharged from pulp and paper industries could cause serious environmental contamination. Appropriate effluent treatment is required to reduce the pollution. Investigations on anaerobic bacteria capable of degrading KL are beneficial to both lignin removal and biofuel regeneration from the effluent. In this paper, an anaerobic strain capable of degrading KL was isolated from the sludge of a pulp and paper mill and identified as Dysgonomonas sp. WJDL-Y1 by 16S rRNA. Optimum conditions for KL degradation by strain WJDL-Y1 were obtained at initial pH of 6.8, C:N ratio of 6 and temperature of 33°C based on statistical analyses by Response Surface Methodology (RSM). For 1.2g/L KL solution, COD removal rate of 20.7% concomitanting with biomass increase of 17.6% were achieved after 4 days incubation under the optimum conditions. After the treatment by strain WJDL-Y1, KL was modified and degraded.