Abstract: Two efficient polyphosphate accumulating organisms, A and E, were screened from the returned sludge which comes from the final sedimentation tank in Beijing Gaobeidian Sewage Treatment Plant. At the same time, the reversing dilution plate separation technology was identified to be beneficial to screening the polyphosphate accumulating organisms. Observations of their morphological, physiological and biochemical features indicate that they are acinetobacter sp. By experiment, the optimal choices for carbon of the polyphosphate accumulating organisms A and E are CH₃COONa and C₅H₈NNaO₄, respectively. Experimental data show the best growth conditions of polyphosphate accumulating organisms in reducing carbon concentrations, i.e. less than COD 100 mg·L^-1:the optimal pH values and temperatures of the polyphosphate accumulating organisms A and E are 8 and 7, 20℃ and 25℃, respectively. Metal ions Mg²⁺, K⁺ and Mn²⁺ can be helpful to accumulate polyphosphate. The effect of oxygen on the phosphate accumulating microorganisms was discussed, and the characteristics of P removal in anaerobic condition and P uptake in aerobic condition could be observed.