Several herbal medicines improve hyperlipidemia, diabetes and cardiovascular diseases. However, the molecular mechanism underlying this improvement has not yet been clarified. In this study, we found that several isoprenols, common components of herbal plants, activate human peroxisome proliferator‐activated receptors (PPARs) as determined using the novel GAL4 ligand‐binding domain chimera assay system with coactivator coexpression. Farnesol and geranylgeraniol that are typical isoprenols in herbs and fruits activated not only PPARγ but also PPARα as determined using the chimera assay system. These compounds also activated full‐length human PPARγ and PPARα in CV1 cells. Moreover, these isoprenols upregulated the expression of some lipid metabolic target genes of PPARγ and PPARα in 3T3‐L1 adipocytes and HepG2 hepatocytes, respectively. These results suggest that herbal medicines containing isoprenols with dual action on both PPARγ and PPARα can be of interest for the amelioration of lipid metabolic disorders associated with diabetes.