Abstract: Objective : To investigate the anticancer function and mechanism of adenosine triphosphate magnesium chloride ATP-M_gCl₂)on lung adenocarcinoma cell. Methods : Compared with ATP, inhibiting rate of lung adenocarcinoma cell line(A549) was measured by cell counting and telomerase activity of the cancer cell line was measured by Telomeric Repeat Amplification Protocol (TRAP) assay after operated by ATP-M_gCl₂. Results : The growth of cancer cells was in-hibited markedly by ATP-M_gCl₂ P<0.01), lots of cells were killed ultimately. ATP-M_gCl₂ showed higher growth inhibition rate and cytotoxic activity than ATP in the first two days P<0.05). Posi-tivities for telomerase activity in ATP-M_gCl₂ and ATP groups were significantly lower than the control group P<0.01), but there was no marked difference between ATP-M_gCl₂ and ATP groups P>0.05). Conclusion : According to these results, we think ATP-M_gCl₂ shows a marked inhibito-ry and cytotoxic activity in a human adenocarcinoma cell line (A549). Its anticancer mechanism is similar to ATP, is relevant to inhibiting the activity of telomerase in cancer cell. But because M_gCl₂ can form an active compound with ATP, which increases the anticancer function of ATP, ATP-M_gCl₂ has a preferable clinical value.