As a novel membrane bioreactor (MBR) system, membrane granular sludge bioreactor (called MGSBR) had not only good performance of pollutant degradation in synthetic wastewater, but also alleviated membrane fouling. The study on the stability of aerobic biogranules followed the investigation of MGSBR performance will pay more attraction and potential to this technology during the wastewater treatment in the future. Although the granules had smaller average diameter, poorer settleability and of a sort sludge activity with 2.0mm of the average diameter, 70 +/- 10 mL gSS(-1) of SVI and 0.83 of VSS/SS ratio, respectively, the results presented in this paper demonstrated that some characteristics of aerobic biogranules in MGSBR system were ultimately preserved. Changes in characteristics of aerobic biogranules were more or less associated with the overgrowth of filamentous bacteria (showed by SEM observation), which was a phenomenon occurred under the combined effects of continuous aeration mode, reduced DO concentration, long SRT and high EPS concentration in MGSBR. Much research should be performed in the future to control the overgrowth of filamentous bacteria in MGSBR system. (c) 2006 Elsevier B.V. All rights reserved.