RAN binding protein 9 (RANBP9) is widely expressed in mammalian tissues, including osteosarcoma, lung, gastric and breast cancer tissues. However, currently, not much is known about the role of RANBP9 in colorectal cancer (CRC). In the present study, RANBP9 expression in CRC tissues and cell lines was measured by immunohistochemistry and western blotting, respectively. Subsequently,
RANBP9
-short hairpin RNA (shRNA) and
RANBP9
plasmids were constructed and transfected into HCT116 and HT29 cells. The effects of RANBP9 knockdown were assessed by Cell Counting kit-8 and colony formation assays, and its effects on tumorigenicity in a nude mouse animal model were investigated. The effect of
RANBP9
-shRNA on cell cycle progression was analyzed by flow cytometry, while cell cycle-associated protein expression levels were examined by western blotting. Compared with in paired normal mucosa, RANBP9 was overexpressed in CRC tissues. Inhibition of RANBP9 in HCT116 and HT29 cells significantly promoted cell growth, colony formation and S phase transition, and increased tumorigenesis
in vivo
. Accordingly, RANBP9 overexpression inhibited cell growth and colony formation. Knockdown of
RANBP9
was associated with upregulated cyclin A2 in the two cell lines. In conclusion, RANBP9 served an inhibitory role in CRC
in vitro
and
in vivo
. Therefore, RANBP9 may be considered a potential target for treatment of CRC.