Recently we isolated CN-3, a new asterosaponin from starfish Culcita novaeguineae, and reported that asterosaponin arrests glioma cell cycle via SCUBE3. However, the multiple mechanisms underlying CN-3 anti-glioma action remains poorly known. Thus, the focus of this study was to evaluate the inhibitory effect of CN-3 on human glioma cells and its underlying molecular mechanisms. U87 and U251 cells were incubated with various concentrations of CN-3, and CCK-8, transmission electron microscopy, ICELLigence, TUNEL, flow cytometry, N-acetyl-<small>L</small>-cysteine, and western blot were conducted. As a result, it was found that CN-3 significantly inhibited U87 and U251 cell viability and proliferation in a time- and dose- dependent manner, and also induced mitochondrial apoptosis. Furthermore, we detected that CN-3 downregulated PI3K, P-Akt, AKT and BCL-2, and upregulated cytochrome C and BAX in U87 and U251 cells. Moreover, ROS triggered the inhibition and cell apoptosis for CN-3 via inactivation of P-Akt and activation of cytochrome C. In conclusion, these findings suggest that CN-3 may be a promising candidate for the development of a therapy of glioma.