A sequencing batch reactor (SBR) was operated in the conventional anaerobic–aerobic mode for enhanced biological phosphate removal (EBPR) using acetate as the sole substrate. Results showed that, however, the reactor was unable to remove phosphate from wastewater. The sludge containing 1.65% of phosphate did not exhibit the typical characteristics of polyphosphate-accumulating organisms (PAO) or glycogen-accumulating organisms (GAO). Phylogenetic analysis, based on 16S rDNA sequences of individual microorganisms, showed that the microbial community of this acetate-degrading sludge was closely related to Comamonas testosteroni (43.8% of total population) of b-1-proteobacteria, Zoogloea resiniphila (25.0%) of b-2-proteobacteria, and Xanthomonas maltophilia (19.8%) of g-proteobacteria. Results of this study imply that GAO might not be the sole group of bacteria responsible to the deterioration of phosphate removal efficiency in an EBPR reactor.