Abstract: Ferulate 5-hydroxylase (F5H) is a key enzyme involved in the phenylpropane metabolism pathway. Based on our previous transcriptome sequencing study, F5H played a negative regulatory role in glycyrrhizic acid (GA) biosynthesis. Therefore, in this study we cloned the F5H gene and investigated its regulatory effect on GA accumulation through gene overexpression and knockout. F5H was cloned from Glycyrrhiza glabra L. (GenBank Accession No. MK882511). A plant binary expression vector pCA-F5H was constructed by inserting F5H into pCAMBIA1305.1 at Spe I and Bgl II sites. The sgRNA sequences were designed based on the first exon of F5H. The CRISPR/Cas9 gene editing vector pHSE-F5H was constructed by inserting F5H sgRNA into pHSE401 at two Bsa Ⅰ sites. PCA-F5H and pHSE-F5H were transfected into Agrobacterium tumefaciens ATCC15834, which was used to induce hairy root overexpressing or knocking out F5H with licorice hypocotyl as explants. At the same time, wild type and negative control hairy roots were also generated. UPLC was used to assay the GA content in different hairy root lines, and results showed that the GA content in hairy root lines knocking out F5H was significantly higher, whereas in hairy root lines overexpressing F5H GA content was lower than that in the wild-type and negative control. In this work, through a reverse genetics strategy, the negative regulatory effect of F5H on GA biosynthesis was confirmed through gene overexpression and knockout. This work will lay a foundation for further elucidation of the molecular regulatory network of GA biosynthesis.