This paper indicates that activated sludge under certain conditions can achieve levels of polyhydroxyalkanoates (PHA) accumulation which would enable the economic recovery of this precursor of biodegradable plastics. The effects of C/N ratio and temperature on polyhydroxyalkanoates production were evaluated. Acetate uptake, ammonium consumption, oxygen uptake and PHA production were studied under aerobic, growth rate limiting conditions. Sludge fed with acetate showed the capability to accumulate PHA to about 6% and 20.5% of cell dry weight at 30 °C and C/N =21.74 after 42 and 72 h, respectively. The accumulation of PHA strongly depends on temperature, with less PHA formation at higher temperature. The average values of maximum growth rate (q„•Cx), affinity constant (K02) and kLa were determined 0.266 mgl-Y , 0.556 mgt' and 0.1422 s-1, respectively.