For the first time, a systematic approach was conducted to determine the key factors influencing the kinetics of hydroxyalkanote (HA) extraction in biological systems. Six mixed microbial systems where polyhydroxyalkanoate (PHA) is produced were evaluated. Experiments were carried out for full-scale and lab-scale activated sludge systems using different configurations (containing floccular or granular sludge), as well as specific PHA accumulating cultures that contain high or low intracellular PHA fractions. The overall reaction was limited by the kinetics of the PHA hydrolysis in floccular cultures, whereas in granular cultures, it was limited by the cell lysis step. The monomeric composition of the polymer also had an impact on the HA extraction rate: higher acid concentration and a longer digestion time should be employed when cells accumulate monomers with more substituents, such as hydroxy-2-methylbutyrate (H2MB) and hydroxy-2-methylvalerate (H2MV). This study optimised the method for HA extraction, which impacts the assessment of the quantity and quality of PHA biopolymers. (C) 2013 Elsevier Ltd. All rights reserved.