LB4, a phosphate-accumulating strain with the ability of poly–β–hydroxybutyrate(PHB) granules accumulation, was isolated from activated sludge of SBR in treatment equipment of wastewater. Through the analysis from morphological, biochemical characteristics, and identification using 16S rDNA sequence approach, LB4 was proved to be a subspecies of Acinetobacter baumannii. The influence factors for PHB accumulation were investigated by alternative cultivation of anaerobic-aerobic cycle. The results showed that the favourite conditions for the strain to accumulate PHB at the beginning of anaerobic phase was at temperature 35 ℃, pH 8.0, COD 2 000 mg/L, and with short-term phosphorus inhibition, the maximum accumulation of PHB could reach to that of 32.6% dry weight of the strain.