Anaerobic membrane bioreactors (anMBR) are increasingly used in wastewater treatment processes. These reactors aim to increase treatment efficiency by combining membrane filtration with biological treatment. In this context, many factors need to be taken into consideration in order to effectively maintain the biological processes taking place in reactors. Water temperature is one of these factors and can significantly affect treatment performance by directly affecting the metabolism of microorganisms. It is known that an increase in water temperature improves the performance of bacteria used in the treatment process. In the current study, it was observed that physical properties changing with temperature slightly reduced treatment performance and it was concluded that the appropriate treatment temperature value is 35 °C, which is still valid in practice. This result provides critical information for optimizing anMBR systems and opens the door to new research on how certain temperature ranges can increase the effectiveness of treatment processes.