Lung cancer is one of the most lethal cancers in China because of its high incidence and highmortality.Ornithine decarboxylase (ODC),an important enzyme in polyamine biosynthesis,is increased incancer cells.Some chemotherapeutic agents aimed at reducing ODC expression show inhibitory effects oncancer cell growth,so ODC can be useful in gene diagnosis and gene therapy of cancers.In this study,weexamined the effect of antisense ODC on lung cancer cells.A-549 cells were infected with rAd-ODC/Ex3as,a recombinant adenovirus containing the cytomegalovirus promoter,green fluorescent protein gene and 120bp antisense ODC.The cell cycle was evaluated by flow cytometry.A nude mouse xenograft model wasused in the tumorigenicity test.Reverse transcription-polymerase chain reaction,Western blot and immuno-histochernistry were used to study the expressions of ODC on lung cancers.It was found that the growth ofcells infected with rAd-ODC/Ex3as was substantially inhibited and cells were arrested at G_1 phase.Cellsinfected with rAd-ODC/Ex3as can suppress tumor formation in a nude mouse xenograft model.Theexpression of ODC mRNA and ODC protein levels in lung cancer tissues was significantly higher than thatin normal tissues (P<0.05),which correlated significantly with the stage of lung cancer (P<0.05).This studysuggested that rAd-ODC/Ex3as has antitumor activity in human lung cancer cells.The ODC gene might playan important role in lung cancer and the overexpression of ODC might be related to the occurrence anddevelopment of lung cancer. Lung cancer is one of the most lethal cancers in China because of its high incidence and high motality. Ornithine decarboxylase (ODC), an important enzyme in polyamine biosynthesis, is increased incancer cells. Home chemotherapeutic agents aimed at reducing ODC expression show inhibitory effects oncancer cell growth, so ODC can be useful in gene diagnosis and gene therapy of cancers. In this study, weexamined the effect of antisense ODC on lung cancer cells. A-549 cells were infected with rAd-ODC / Ex3as, a recombinant adenovirus containing the cytomegalovirus promoter, green fluorescent protein gene and 120 bp antisense ODC. The cell cycle was evaluated by flow cytometry. A nude mouse xenograft model was used in the tumorigenicity test. Reverse transcription-polymerase chain reaction, Western blot and immuno-histochernistry were used to study the expressions of ODC on lung cancers. It was found that the growth of cells infected with rAd-ODC / Ex3as was substantially inhibited and cells were arrested at G_1 phase.Cellsinfected with rAd-ODC / Ex3as can suppress tumor formation in a nude mouse xenograft model. Theexpression of ODC mRNA levels in lung cancer tissues was significantly higher than thatin normal tissues (P <0.05), which correlated significantly with the stage of lung cancer (P <0.05). This studysuggested that rAd-ODC / Ex3as has antitumor activity in human lung cancer cells. The ODC gene might play important role in lung cancer and the overexpression of ODC might be related to the occurrence and development of lung cancer.