Conventional desizing of cotton is employed since several decades by the use of ??-amylases, which hydrolize water-insoluble starch to water-soluble oligosaccharides. This enzymatic desizing process leads to waste waters with an extremely high chemical oxygen demand (COD) due to its high sugar content. Nowadays, these liquors are still disposed without use resulting in an ecological questionable pollution and high emission charges for cotton finishing manufacturers. Here, an innovative technology for the production of energy from textile waste waters from cotton desizing was developed. Such desizing liquors were fermented by methane-producing microbes to biogas. For this purpose a semi-industrial plant with a total volume of more than 500 L was developed and employed over a period of several weeks. The robust and trouble-free system produces high amounts of biogas accompanied with a significant reduction of the COD of more than 85 %. With regard to growing standards and costs for waste water treatment and disposal the new process can be an attractive alternative for textile finishing enterprises in waste water management combining economic and ecological benefits.