To study the effects of worm predation on membrane fouling in an MBR+worm reactor, an MBR+worm reactor with worm (R1) and an MBR+worm reactor without worm (R2) were operated in parallel. Variation of transmembrane pressure (p_TM) and microbial metabolites were studied in the MBR (S-MBR) of the R1 and the MBR (C-MBR) of the R2. Denatured gradient gel electrophoresis (DGGE) was used for analyzing the composition and distribution of microbial community in the S-MBR and the C-MBR. The results showed that the membrane fouling cycles of the S-MBR and the C-MBR were 90 d and 28-37 d, respectively. Worm predation decreased the polysaccharide and proteins in the soluble microbial products (SMP) and extracellular polymeric substances (EPS) of the S-MBR. Alphaproteobacterium, Betaproteobacterium, Deltaproteobacterium, Geobacter on the membrane wire surface of the S-MBR and Azorhizobium, Rhodobacter, Gammaproteobacterium, Flavobacteria on the membrane wire surface of the C-MBR played an important role in the membrane fouling. Caldilinea was suggested to be related to the membrane fouling alleviation of the S-MBR. Worm predation changed the microbial community structure of the S-MBR, resulting in membrane fouling alleviation.