Polyhydroxyalkanoates (PHAs) are biodegradable and environmentally friendly natural polymers. In this study, we isolated a bacterium strain capable of synthesizing PHAs from the aerobic sludge of a sewage treatment plant. The bacterium was identified as Burkholderia cepacia via physiological and biochemical tests as well as 16S rDNA sequence analysis. Strain WN-H(4)1 produced PHAs, which was identified as P3HB. These PHAs have a number average molecular weight of 2.6 x 10(4) Da, a polydispersity index (PDI) of 2.4, and its thermal properties include a glass transition temperature of 1 A degrees C, a melting temperature of 171 A degrees C, and a decomposition temperature of 280 A degrees C. These properties indicate that P3HB produced by WN-H(4)1 has a high purity and good thermal stability.