Abstract: AimTo examine the effect of inducible nitrogen monoxide synthase (iNOS) on tumour cells chemosensitivity to mitomycin C (MMC) analogue 5-aziridinyl-3-hydroxyl-1-methylindole-4,7-dione (629) in vitro, and elucidate the possible role of iNOS in the metabolism of 629. Methods Human sarcoma cells (HT1080) and its iNOS gene transfected clones (iNOS9, iNOS12) were exposed to 629 at concentrations of 1 nmol·L^-1-100 μmol·L^-1. 3-［4,5-Dimethylthiazol-2-yl］-2,5-diphenyl-tetrazolium bromide (MTT) assay, agarose electrophoresis and flow cytometric analysis were used to determine cell sensitivity, deoxyribonucleic acid (DNA) damage and the change of cell cycle in above process, respectively. All experiments were performed both in air and under hypoxia parallelly. Results 629 was more toxic than MMC, and enhanced cytotoxicity under hypoxia, which resulted in cell necrosis. Sixteen hours after treated with 629, HT1080 cells and related iNOS-transfected clone cells were obviously blocked in G₂/M phase. ConclusioniNOS plays dual roles in 629 metabolism, enhancing or decreasing the cytoxicity of 629 depending on the intracellular oxygen pressure P_O2, which caused higher cytotoxicity to hypoxia cells of 629 with the increasing of iNOS activity.