Abstract: Tannery wastewaters are highly complex and are characterized by high contents of organic, inorganic and nitrogenous compounds, chromium, sulfides, suspended solids and dissolved solids. Treatment of tannery wastewater is carried out by physical or chemical or biological or combination of these methods. This study reviews various biological treatment methods applied for tannery wastewater. Characteristics of wastewaters from different tanneries and various methods for treating these tannery wastes are discussed. It was noted that the Chemical Oxygen Demand (COD) removal efficiencies and process capacities were affected by the variations in organic loading rates, presence of chromium and sulfides. The review shows that all aerobic processes have a similar level of COD removal, but the highest COD removal efficiency at a high organic loading rate was observed in anaerobic reactors. Upflow Anaerobic Sludge Blanket Reactor (UASB) exhibited better performance for treating high strength tannery wastewater effectively, compared with conventional reactors. Both aerobic and anaerobic processes are employed for the treatment of tannery wastewater. From the review it can be concluded that physical/chemical processes combined with biological process is the better option for the treatment of tannery wastewater.