Objective: To investigate apoptosis and related molecular mechanism caused by nano FeOx powders in hepatoma cell lines HepG2 and Bel-7402 exposed to extremely low frequency altering magnetic field (EMF). Methods: Proliferation and apoptosis of cell lines were detected by CCK-8 kit and flow cytometer using a apoptosis kit,respectirely. Western blot was utilized to detect expression of protein associated with apoptosis and heat shock protein. Results: The proliferation of cells absorbed by nano FeOx powders was inhibited due to the EMF exposure, the inhibited ratio of HepG2 and Bel-7402 cells were (35.54±3.2)% and(76.31±2.3)%(P < 0.05), respectively. The exposure of EMF induced early apoptosis of cells, the apoptosis ratios of HepG2 and Bel-7402 absorbed by nano powders were(18.64±6.68)% and (23.34±2.16)%,respectirely(P > 0.05). Western blot was utilized to analyze the mechanism of cells apoptosis, and the results indicated that the expression of Bcl/Bax in Bel-7402 cells was had no difference, but the apoptosis ratio was similar in two cell lines the expression of Hsp-27 in Bel-7402 was higher than HepG2 cells. Conclusion: The inhibition of proliferation and kigh early apoptosis of Bel-7402 and HepG2 loading magnetic nano FeOx powders under EMF exposure indicated that this kind of treatment could be applied as a potential method for treatment of liver tumor in future.