Inducible nitric oxide synthase (iNOS) is the key enzyme in NO synthesis and exhibits a high expression in numerous types of malignant tumors. Previous studies have demonstrated that iNOS promotes the production of tumor blood vessels by catalyzing the synthesis of additional NO. Certain experimental evidence has suggested that iNOS may regulate the levels of vascular endothelial growth factor (VEGF), as the level of VEGF may be induced by iNOS during endothelial cell migration and angiogenesis. In this study, it was observed that SiHa and HeLa cells exhibit depressed proliferation levels following the knockdown of iNOS with a lentivirus. In addition, NO levels demonstrated a correlation with VEGF levels in the cell culture supernatant.