The cultivation of aerobic granules in SBR by seeding anaerobic granular sludge was investigated using acetate-based synthetic wastewater. Morphological variation of granular sludge in the reactor was observed and results revealed that the inoculated anaerobic granules experienced a process of disintegration-recombination-growing up. The disintegrated anaerobic sludge may play a role of nucleus for the granulation of aerobic sludge. The sludge concentration increased for the first 4 weeks, then decreased and reached a stable value of 5 g/l at 60 d with a SVI of 30-40 ml/g. Granular sludge dominated in the reactor and suspended sludge concentration was less than 0.5 g/l at the end of the process. In the inoculated anaerobic granular sludge, spherical bacteria were the main microorganisms, however, rod-shaped and filamentous microorganisms prevailed in the cultivated aerobic granules. This is ready way to cultivate aerobic granules by seeding anaerobic granular sludge. (C) 2003 Elsevier Ltd. All rights reserved.