Anaerobic digestion of acidic cottage cheese whey shows two advantages: pollution reduction and biogas production, which could be used as energy source to reduce energy consumption of the plant. Acid whey contains about 5% lactose, 0,5% protein, 0,05% fat and is characterized by high COD concentration (70 g/L). Acid whey is usually used for animal feeding but the transportation cost is high thus it is rather attractive for energy production. Anaerobic digestion is the breakdown of biodegradable materials, mostly complex organic material, into methane, carbon dioxide and water by microorganisms in the absence of oxygen [1]. The anaerobic digestion process is carried out by a consortium of interdependent and symbiotic microorganisms. In this study the bioreactor had a total working volume of 6 L. The temperature was kept at 37 oC with standard deviation of 0,2 oC. The substrate was mixed all the time with stirring speed of 40 rpm. The initial pH of the 1 L raw whey was 4,6 which was increased to 7,0 by addition of 3M NaOH. After addition of 1 L inoculum (slurry from working pilot plant (50 L)) pH increased till 7,3. 3M NaOH was used to control pH at 7,2. The retention time was 10 days.