Natural product Tanshinone IIA (TanIIA) induces apoptosis and differentiation in hepatocellular carcinoma (HCC) cells, but its clinical use is limited due to poor water solubility and lack of appropriate formulations for drug delivery. In this study, we capsulated TanIIA into a microemulsion (ME) that was composed of phospholipid, ethyl oleate, glycerol and pluronic F68. We then determined the anticancer effects and mechanisms of action for TanIIA ME with in vitro and in vivo HCC models. The mRNA and protein levels of apoptosis-related molecules (Bcl-2, Bax and caspase-3) were analyzed in murine hepatoma H22 cells and H22 tumor-bearing mice by flow cytometry, RT-PCR and immunofluorescence staining. Compared with the groups treated with empty ME and drug solution, the mRNA levels of Bax and caspase-3 were up-regulated, and the mRNA and protein levels of Bcl-2 were down-regulated in H22 cells treated with TanIIA ME in a dose-dependent manner. The mRNA and protein levels of Bax and caspase-3 were up-regulated and the Bcl-2 levels were also down-regulated in animals treated with TanIIA ME in a dose-dependent manner. Our results suggest that as a novel drug delivery system, microemulsion enhances the antitumor effects of TanIIA.