Ebrahimi et al. (2010) reported that start-up seed sludge applied to the system at 30°C had failed to obtain a stable aerobic granular sludge. Cultivation of a stable aerobic granular sludge at 30°C and 35°C were only achievable by running the reactor at 20°C using inoculum sludge and gradually increasing the temperature. The same technique had been applied by de Kreuk et al. (2005b) who also failed to develop aerobic granular sludge at low temperature during the start-up at 8°C. Nevertheless gradually decreasing the temperature from a start-up at 20°C to 8°C, contributed in running the system successfully. In this study, cultivation of aerobic granular sludge with a start-up at different high temperatures which were 30°C, 40°C and 50°C demonstrated positive results to obtain stable granules with excellent nutrients removal performances. Establishment of organics, biological phosphorus and nitrification required short period of time for the acclimatization phase due to the change of circumstances (e.g. the composition of synthetic domestic wastewater and the operation mode of SBR). However, considering the inoculation sludge used in this research was taken from wastewater treatment plant (WWTP) located in the Madinah city, Saudi Arabia with daytime temperatures averaging about 40–50°C and nights about 28°C, it was an advantage that the inoculum sludge used was well-adapted to high temperatures. This shortened the time needed for the system to achieve stable removal performances.