Abstract: Objective To explore the effect of de novo methylation of c-myc, p16 promoter regions on the growth of cancer cell line MGC803, and to search a new target for diagnosis and treatment of cancers. Methods MGC803 was exposed to the methyl donor SAM to methylate the promoter regions of c-myc and p16. Growth speed of the cells was evaluated by MTT assay, and the expression of c-myc and p16 were determined by immunohistochemistry. Results Treated by SAM, MGC803 grew more slowly; the expression of c-myc was obviously decreased (P<0.05). However there was no significant difference in expression of p16 (P>0.05). Conclusion SAM could effectively decrease the growth of the cancer cells by inhibiting the transcription activity and expression of c-myc without altering the tumor suppressor gene p16, which indicated its function in the treatment of cancer.