Dissolved organic nitrogen can cause undesirable environmental problems in aquatic environments, such as eutrophication, nitrogenous disinfection by-product formation, and a decrease in the amount of dissolved oxygen. 25–80% of the total dissolved nitrogen (TDN) in the effluent of wastewater treatment plants is dissolved organic nitrogen (DON) form. As a result of these concerns, the biodegradability and management of DON is important issue for domestic/industrial wastewater treatment. Dairy products are widely consumed in Turkey and dairy industry wastewater has a high organic nitrogen content. In this study, the biodegradability of wastewater samples obtained from yoghurt and cheese production industries was investigated. The biodegradability of wastewater samples was determined by using a mixed bacteria culture and identified between 72.2 and 81.7% for yoghurt production wastewater and 19.1–20.1% for cheese production wastewater. BDON/TDN ratio was found as 65.4–71.9% and 16.5–17.5% ranges for yoghurt and cheese production wastewaters, respectively. Although both are released from dairy production, it has been determined that white cheese production wastewater has a very low biodegradability compared to yoghurt production wastewater. It is thought that the results of this study will contribute to the evaluation of the removal efficiency in other industrial facilities and domestic wastewater treatment plants.