Abstract: Recent studies have demonstrated that nitrite and ammonia levels are higher in the tumor environment, but their effects on cancer cells remains unclear. The present study was designed to determine the effects of nitrite and ammonia on tumor invasion and the role of reactive oxygen (ROS)/ornithine decarboxylase (ODC) pathway. SMMC-7721 cells were treated with sodium nitrite, ammonium chloride, sodium nitrite and ammonium chloride mixture for 24 h, the cell viability was analyzed using the MTT assay, cell invasion was analyzed with the transwell assay, the intracellular ROS levels were detected with a reactive oxygen species (ROS) test kits, the expression of intracellular ODC was examined with immunofluorescence and Western blot, the expression of matrix metallopeptidase-2(MMP-2) and MMP-9 were analyzed by Western blot. Compared with the control group, SMMC-7721 cells exhibited an increase in cell viability, invasion ability, ROS levels and ODC protein after exposure to 150 μmol·L^-1 sodium nitrite and ammonium chloride mixture for 24 h. The invasive activity was reduced by ROS scavenger N-acetycysteine (NAC) in SMMC-7721 cells. The specific ODC inhibitor difluoromethylornithine (DFMO) increased ROS levels and weakened the ability of sodium nitrite and ammonium chloride mixture in the regulation of invasion of SMMC-7721 cells. These data demonstrated that sodium nitrite and ammonium chloride mixture promote invasion of SMMC-7721 cells by enhancing ROS/ODC pathway.