Objective:To explore the in vitro and in vivo inhibitory effects of deuterium-depleted water (DDW) on the proliferation of human lung carcinoma cells, and to explore the possible mechanism. Methods: The inhibitory effect of DDW on the proliferation of human lung carcinoma A549 cells and human embryonic lung fibroblast HLF-1 cells was examined by MTT assay; apoptosis of A549 cells was examined by TUNEL; and cell cycle was analyzed by flow cytometry. Mouse model of lung carcinoma was established by inoculating human lung carcinoma H460 cells into BALB/c nude mice, and the growth of implanted tumors was observed after DDW treatment for 60 d. Results: Compared with control group, A549 cells treated with 0.0025％, 0.0050％ or 0.0105％ DDW showed significantly decreased proliferation 10 h after treatment (P<0.01). Then the inhibitory effects of DDW gradually disappeared, but appeared 48 h later again, with the inhibitory effects at 72 h being significant (P<0.05). DDW at the same dosages showed no inhibition on the proliferation of HLF-1 cells (P>0.05). TUNEL assay verified the apoptosis of DDW-treated A549 cells, and the apoptosis rate of DDW-treated A549 cells was significantly higher than that of control group（[45.30±4.21]% vs [22.25±030]%, P<0.01). Cells in S phase were significantly increased in DDW-treated A549 cells compared with those in the control group (P<0.05). The life quality of H460 cell-inoculated nude mice treated with DDW was greatly improved, with the tumor inhibition rate being 30.08%. Conclusion: DDW can inhibit the proliferation of lung cancer cells within a certain range of dosage and in a fluctuating pattern; its mechanism might be associated with induction of apoptosis and cell cycle arrest in S phase of tumor cells.