A free fatty acid-containing substance, which is a waste liquid or by-product obtained in a process for producing palm oil or which is a hydrolysate of the waste liquid or by-product, is subjected to distillation treatment to obtain a free fatty acid fraction satisfying the requirements (i), (ii) and (iii), and a polyhydroxyalkanoate-producing microorganism is cultured in a culture solution containing the free fatty acid fraction. (i) The content of squalene is 0.05 wt % or less. (ii) The ratio of a peak area of trimethylindene to a peak area of a naphthalene-d8 standard is 110 or less in first-dimensional dynamic headspace-GC/TOFMS analysis. (iii) The ratio of a peak area of butyric acid to a peak area of a naphthalene-d8 standard is less than 10 in first-dimensional dynamic headspace-GC/TOFMS analysis.