This work was undertaken to develop an improved gas chromatography (GC) analysis of poly (3-hydroxyalkanoate) (PHA) quantification method based on acidic methanolysis. This is achieved by investigating the kinetics of acidic hydrolysis of PHAs with sulfuric acid in the chloroform/aqueous solution to identify suitable hydrolytic pretreatment conditions for quantitative analysis of PHAs. The target parameters included sulfuric acid concentration, salt (NaCl) addition, kind of PHAs (commercial products of poly-3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV-8%) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx-3.8% and-10.5%), as well as the type of PHA-producing microorganisms (Cupriavidus taiwanensis 184 and Burkholderia sp. PTU9). These results show that esters would preferentially accumulate in the organic phase when NaCl was added in the two-phase system, thereby enhancing the accuracy of GC analysis. Decomposition efficiency of different types of PHAs was found to be dependent on sulfuric acid concentration, such as 1% H2SO4 was favorable for PHB decomposition, while 5 and 7% H2SO4 should be used to decompose PHBV and PHBHHx. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.