This study aimed to investigate the ability of Citrobacter sp. strain L17 to decolourise azo dye in a rich medium (MP5) and three different minimal media (MMP5, MMGF11 and MM63) under microaerophilic and anaerobic conditions. Amaranth was used as the model dye in this investigation. Under microaerophilic condition, reactions were carried out at two different temperatures; 37°C and 45°C, whereas experiments with anaerobic condition were conducted only at 37°C. Results showed that, under microaerophilic condition, full decolourisation of Amaranth was achieved in all media tested at 37°C. However, at 45°C, complete decolourisation was observed only in MP5, MM63 and MMGF11 but no obvious decolourisation occurred in MMP5. On the other hand, complete decolourisation was observed in all media tested under anaerobic condition at 37°C, with the fastest decolourisation in MP5 (rich medium containing glucose and nutrient broth) and the slowest in MMP5. It was found that an inorganic buffer containing glucose at lower concentration was sufficient to achieve complete decolourisation under anaerobic condition. This finding is essential to identify a suitable medium for future study on biogas production by dye-degrading bacteria, which mostly requires anaerobic conditions.