AIM: To determine the expressions of inducible nitric oxide synthase (iNOS) and matrix metalloproteinase-9 (MMP-9) in hepatocellular carcinoma (HCC) and to investigate the relationship between iNOS and MMP-9 expression and their effects on angiogenesis and progression of HCC. METHODS: In this study, we examined iNOS, MMP-9, and CD34 expression in specimens surgically removed from 32 HCC patients and 7 normal liver tissues by immunohistochemical staining. Meanwhile, microvessel density (MVD) was determined as a marker of angiogenesis by counting CD34-positive cells. RESULTS: The positive rates of iNOS and MMP-9 expression were 71.88% (23/32) and 78.13% (25/32) in HCC. MMP-9 expression was significantly correlated with tumor size, capsule status, TNM stage, and risk of HCC recurrence (P= 0.032, P= 0.033, P= 0.007, and P= 0.001, respectively). There was also a significant relationship between iNOS expression and capsule status and risk of HCC recurrence (P= 0.049 and P= 0.004, respectively), but no correlation between iNOS expression and tumor size and TNM stage. There was a positive association between MVD and TNM stage and risk of HCC recurrence (P= 0.037 and P= 0.000, respectively). The count of MVD was significantly different in different iNOS and MMP-9 immunoreactivity groups (F= 17.713 and 17.097, P= 0.000 and P= 0.000, respectively). The examination of Spearman’s rank correlation coefficient showed that there was a significant positive correlation between MVD and iNOS, MMP-9 immunoreactivity (r= 0.754 and 0.751, P= 0.000 and A=0.000, respectively). There was also a significant association between MMP-9 and iNOS expression in HCC (P= 0.010). CONCLUSION: Nitric oxide (NO) produced by iNOS could modulate MMP-9 production and therefore contribute to tumor cell angiogenesis and invasion and metastasis in HCC. The strong expression of iNOS and MMP-9 in HCC may be helpful in evaluating the recurrence of HCC, predicting poor prognosis. For patients with strong expression of MMP-9 and iNOS, the optimal treatment scheme needs to be selected. AIM: To determine the expressions of inducible nitric oxide synthase (iNOS) and matrix metalloproteinase-9 (MMP-9) in hepatocellular carcinoma (HCC) and to investigate the relationship between iNOS and MMP-9 expression and their effects on angiogenesis and progression of HCC. METHODS: In this study, we examined iNOS, MMP-9, and CD34 expression in specimens surgically removed from 32 HCC patients and 7 normal liver tissues by immunohistochemical staining. Meanwhile, microvessel density (MVD) was determined as a marker of angiogenesis by counting CD34-positive cells. RESULTS: The positive rates of iNOS and MMP-9 expression were 71.88% (23/32) and 78.13% (25/32) in HCC. There was also a significant relationship between iNOS expression and capsule status and risk of HCC recurrence (P = 0.032, P = 0.007, P = 0.001, respectively) = 0.049 and P = 0.004, respectivel There was a positive association between MVD and TNM stage and risk of HCC recurrence (P = 0.037 and P = 0.000, respectively). The count of MVD was significantly different The examination of Spearman’s rank correlation coefficient showed that there was a significant positive correlation between MVD and iNOS, MMP-9 (F = 17.713 and 17.097, P = 0.000 and P = 0.000, respectively) There was also a significant association between MMP-9 and iNOS expression in HCC (P = 0.010). CONCLUSION: Nitric oxide (NO) produced by iNOS (r = 0.754 and 0.751, could modulate MMP-9 production and therefore contribute to tumor cell angiogenesis and invasion and metastasis in HCC. The strong expression of iNOS and MMP-9 in HCC may be helpful in evaluating the recurrence of HCC, predicting poor prognosis. For patients with strong expression of MMP-9 and iNOS, the optimal treatment scheme needs to be selected.