. sludge. Nevertheless, quantitative PCR method for Candidatus ‘Accumulibacter phosphatis’ has not been developed yet. In this study, quantitative PCR method for Candidatus ‘Accumulibacter phosphatis’. quantitative PCR was 1.0 % for Ct value and 11 % for the calculated copy numbers, respectively (n=6). Variation in quantitative PCR only was 0.78 % for Ct value and 7.5 % for the calculated copy. sludge samples were quantified both by the quantitative PCR method and by the FISH method. The quantification results by these two methods agreed satisfactorily, with an R2 value of 0.6871...