MicroRNAs are emerging as important endogenous regulators of gene function and they are playing an important role in the occurrence and development of cancer. They are also regarded as robust biomarkers of cancer diagnosis and prognosis. Hepatocellular carcinoma (HCC) is a common and complex human malignancy with high mortality and morbidity in the world. MicroRNA-122 (miR-122) is a liver-specific microRNA and is closely associated with HCC metastasis, which makes miR-122 a promising target for drug design and development. In this study, we performed a cell-based screening method for discovering miR-122 activators and found that oleanolic acid (OA), a natural pentacyclic triterpene, specifically increased miR-122 expression in a concentration-dependent manner. Two HCC cell lines (HepG2 and Sk-hep-1 cells) were used to evaluate the effect of OA on cell migration and invasion abilities. The results indicated that OA attenuated the migration and invasion abilities of HCC cells by upregulating miR-122 expression. In addition, OA increased the expression of E-cadherin and decreased the expression of β-catenin, N-cadherin and vimentin. After knocking down miR-122 with miR-122 inhibitor, we found that the effect of OA on these epithelial-to-mesenchymal transition (EMT) related molecules was significantly weakened, indicating OA exhibited anti-EMT effect by increasing the expression of miR-122. These finding may help to better understand the molecular mechanism of OA's anti-metastasis activity.