We found siRNA-DNMT1, resemble to the 5-Aza-CR, could effectively demethylate the TSGs (e.g. RASSF1A and APC) to recover the tumor suppressive ability, but the treatment of siRNA-DNMT1 had less cytotoxicity than 5-Aza-CR which showed the potential superiority in lung cancer-therapy. The gene discussed is RASSF1; the disease is lung carcinoma.