Ubiquinone, known as a component of the electron transfer system in many organisms, has a different length of the isoprenoid side chain depending on the species, e.g., Escherichia coli, Saccharomyces cerevisiae and humans have 8, 6, and 10 isoprene units in the side chain, respectively. No direct evidence has yet shown what factors define the length of the side chain of ubiquinone. Here we proved that the polyprenyl diphosphate that was available in cells determined the length of the side chain of ubiquinone. E. coli octaprenyl diphosphate synthase (IspB) was expressed with the mitochondrial import signal in S. cerevisiae. Such cells produced ubiquinone-8 in addition to the originally existing ubiquinone-6. When IspB was expressed in a S. cerevisiae COQ1 defective strain. IspB complemented the defect of the growth on the non-fermentable carbon source. Those cells had the activity of octaprenyl diphosphate synthase and produced only ubiquinone-8. These results opened the possibility of producing the type of ubiquinone that we need in S. cerevisiae simply by expressing the corresponding polyprenyl diphosphate synthase.