DDX5, also named RNA helicase p68, is a prototypic member of the DEAD (Asp-Glu-Ala-Asp) box family. DDX5 has been shown to be involved in the processes requiring the alteration of RNA structures, such as the maturation of pre-mRNA, rRNA, and miRNA. DDX5 also plays important helicase-independent roles in transcriptional regulation. DDX5 can act as a transcriptional coactivator of the androgen receptor (AR), estrogen receptor α (ERα), tumor suppressor p53, MyoD, RUNX2, and β -catenin, which are involved in the regulation of cell proliferation, differentiation, and tumorigenesis. DDX5 has been shown to be up-regulated in various cancers, including breast cancer, prostate cancer, and colorectal cancer, suggesting that DDX5 may participate in tumor development. DDX5 can also act as a transcriptional repressor through interacting with HDAC1.