20( S )-Ginsenoside Rh2 (GRh2) and ginsenoside Rg3 (GRg3) are members of the protopanaxadiol family and have been investigated for possible chemopreventive activity. This study explored the biological and apoptotic mechanisms induced by 20( S )-GRh2 in human acute leukaemia line-Reh cells. Reh cells were treated with different concentration of 20( S )-GRh2 in vitro . Cell viability was determined by Cell Counting Kit-8 and Annexin V/7-AAD assays. Mitochondrial membrane potential (MMP) was examined through JC-1 staining. Activation of caspases associated with the mitochondria-mediated apoptosis pathway was determined by Western blot. We observed that survival of Reh cells decreased after exposure to 20( S )-GRh2 in a concentration-dependent manner. Moreover, 20( S )-GRh2 can induce mitochondria depolarization of Reh cells as evident in the shift in JC-1 fluorescence from red to green. In addition, 20( S )-GRh2 induced the release of mitochondrial cytochrome c and activation of caspase-9 and caspase-3 in Reh cells. These results indicate that 20( S )-GRh2 could induce apoptosis through the mitochondrial pathway, demonstrating its potential as a chemotherapeutic agent for leukaemia therapy.