This study was designed to investigate the cytotoxic effect of methanol extract of garlic, onion and those mixture on two kinds of human lung cancer cell lines (NCI-H522, NCI-H596) using MTT assay. MeOH extract of garlic, onion and those mixture showed cytotoxic effect on both NCI_H522 and NCI-H596. The growth of the cancer cells exposed to medium containing garlic, onion extracts and those mixture was inhibited dose-dependently. The growth of NCI-H522 was inhibited more in the garlic extract than in the onion extract, but that of HCI-H596 was inhibited highese in the onion extract. IC50 values of garlic extract on NCI-H522 and NCI-H596 were 0.84 mg/mL, 0.88 mg/mL and those of onion extract were 1.04 and 0.79, respectively. and the mixture of garlic and onion extracts also inhibited the growth of both NCI-H522 and NCI-H596 cells.