Re-activation characteristics of anaerobic granular sludges starved for 10 months were studied. Specific biomass activities were monitored and both scanning and transmission electron microscopies were used to investigate the microbial and the morphological changes in granular sludges during storage. In order to investigate the re-activating capability of granular sludges starved for 10 months, the recovery of microbial activity was observed in a reactor re-feeding test as well as in a serum bottle test (SET). Specific biomass activity tests indicated that the room temperature was preferred to the refrigerated conditions in maintaining the methanogenic activity. The specific biomass activity after IO months of storage decreased by more than 30% of the initial. The re-activating test showed that granular sludge was quickly re-activated by re-feeding the substrate. With 10 months old granular sludge a 11.2 kg COD/m(3).day loading rate was achieved within 12 days after the onset of refeeding. The overall performance of the reactor with granular sludges stored at room temperature was more stable than that at 4 degrees C.