Invasion and metastasis of cancerous cells affects the treatment and prognosis of hepatocellular carcinoma (HCC). HIF-1α-induced epithelial-mesenchymal transition (EMT) is a critical process associated with cancer metastasis. Basil polysaccharide (BPS), one of the major active ingredients isolated from Basil (Ocimum basilicum L.), has been identified to possess an antitumor activity for HCC. In our current study, BPS was obtained by water extraction and ethanol precipitation method and the characterization was analyzed through ultraviolet absorption spectra and Fourier-transform infrared spectrum. A CoCl₂-induced hypoxia model and a HCC cell line-derived xenograft (CDX) model were used to explore the anti-metastasis efficacy and the mechanism that underlies the antitumor activity of BPS. The results showed that hypoxia could facilitate EMT and promote HCC cells migration and/or invasion. Conversely, BPS inhibited the progression and metastasis of tumor, as well as reversed EMT by causing cytoskeletal remodeling under hypoxic conditions. Moreover, BPS alleviated tumor hypoxia by targeting HIF1α, and the mesenchymal markers (β-catenin, N-cadherin and vimentin) were down-regulated, while the epithelial markers (E-cadherin, VMP1 and ZO-1) were up-regulated after BPS treatment under hypoxic conditions. Thus, these results suggested that BPS may be a valuable option for use in clinical treatment of HCC and other malignant tumors.