UASB reactors R-I and R-II each with an effective volume of 6.0liters were used to study the treatability of actual bleaching effluent obtained from NSSC pulp and paper mill at mesophilic temperature and neutral pH. Methanol as a source of an easily biodegradable substance along with an activated carbon of effective size 1.5-2.5mm was added to the reactor R-I to evaluate its efficiency. It was observed that corresponding to an OLR of 2.14kg-COD/m3-day the overall COD removal efficiency of the reactors R-I and R-II was 83% and 64%, respectively. And the AOX removal efficiency was noticed as 71% and 49% for reactor R-I and R-II, respectively. During the study it was observed that the treatability efficiency of reactor R-I was comparatively  better but the amount of its biogas production was slightly lower. The average biogas gas production in reactors R-I and R-II during the course of study was observed as 0.19L/g-CODremoved and 0.32L/g-CODremoved, respectively, with mean methane composition of 58-60% in both the reactors. The results of this study suggest that the use of methanol and an activated carbon in a UASB reactor to biodegrade the bleaching effluent of NSSC pulp and paper mill at mesophilic temperature and neutral pH reactor is a feasible and viable technique.