A gas chromatography-mass spectrometry method for quantification of polyhydroxyalkanoates (PHAs), containing 4-carbon to 16-carbon monomers, even in the absence of standards, was developed. Strong linear correlations existed between PHA carbon number and retention time/response factor (R-2 >= 0.987). Based on the correlations, high recovery values, between 100.5% and 114.3%, were obtained for PHA polymers. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.