Oridonin, an active diterpeniod isolated from Rabdosia rubescens, has been reported for its anti-tumor activity on several cancers, however, its effect on oral squamous cell carcinoma (OSCC) remains unclear. In this study, we demonstrated for the first time that oridonin inhibited the growth of OSCC cells both in vitro and in vivo. Oridonin decreased the proliferation and clonal formation of cultured OSCC cells in a dose-dependent manner. Further study indicated that oridonin induced G2/M phase arrest in OSCC cells, which was associated with the downregulation of proteins related to G2/M transition including cdc25C, cdc2 and cyclin B1, as well as the upregulation of p53 and phosphorylated-cdc2. In addition, we discovered that oridonin induced OSCC cell apoptosis by activating the intrinsic apoptotic pathway, which was indicated by the increased expression of cleaved-caspase 3, cleaved-caspase 9 and proapoptotic protein Bax and reduced expression of caspase 9 and antiapoptotic protein Bcl-xl. Finally, oridonin suppressed the growth of OSCC in an xenograft mouse model. Immunohistochemical analysis showed a reduction of cyclin B1-positive cancer cells and an increase of TUNEL-positive cancer cells in oridonin-treated mice. Therefore, oridonin may be a potentially effective agent for the treatment of OSCC in future.