Polyhydroxybutyrate (PHB)-rich aerobic granule was cultivated in a sequencing batch reactor (SBR) under nitrogen deficient conditions by adapting a two-step strategy. In the first step the PHB-storage ability of activated sludge was enhanced by keeping both oxygen and ammonia at a low level. In the second step granular sludge was cultivated through adjusting sludge settling time. The matured PHB-rich granular sludge with a PHB content of 40 +/- 4.6% and a high settling ability was successfully obtained. The analysis on sludge surface properties showed that the surface charge, extracellular polymeric substances (EPS) content and the sludge hydrophobicity all increased significantly, while the surface energy of sludge decreased to a relatively steady state accompanied with the growth of granular sludge. This study demonstrates that the metabolism of intracellular storages induced microbial production of EPS, which favored the formation of aerobic granules. (c) 2014 Elsevier Ltd. All rights reserved.