Low PHA accumulation is one of the main limitations of the industrial production of polyhydroxyalkanoates (PHA) from mixed cultures. Different PHA yields and physical properties were obtained by varying culture conditions (acetate concentration, nitrogen and phosphate availability, temperature and pH). Glycogen accumulating organisms (GAOs), microorganisms able to create and store PHA, which use acetate as their sole carbon source, were obtained after selection from mixed culture from activated sludge. All PHA presented good adhesion properties and were soluble in halogenated and polar solvents. The maximum PHA storage rate (20 % of cell dry weight) was achieved with a concentration of 4 g/L acetate. The optimum temperature for PHA production was 23 °C (24 % of cell dry weight). Low nitrogen concentration increased the yield (22 %) while phosphate concentration and pH did not influence PHA production. PHA accumulation of almost 30 % was obtained with previously found optimum parameters.