Biological process is an important approach to treat the dye wastewater. The azo dyes decolouration by special azoreductase of different aerobic bacteria and fungi was summarized. Under anaerobic condition, reductive decolourization of azo dyes was carried in the presence of redox mediators which act as electron shuttle. It was also pointed out that azo dye reduction occurred mainly under anaerobic condition. Different electron donor resulted in different decolourization rate. Problems of current biotechnology were analyzed and corresponding measures were discussed.
