The prognosis for hepatocellular carcinoma (HCC) depends mainly on the clinicopathological characteristic regarding invasion and metastasis. In addition, another distinguishing feature of HCC is the high incidence of concomitant liver cirrhosis, in which the extracellular matrix proliferates markedly. Therefore, the present study was designed to investigate the molecules responsible for the invasion potential of HCC by focusing on matrix metalloproteinase (MMP) in particular, MMP-2 and MMP-9 and the corresponding tissue inhibitor of metalloproteinase (TIMP-2 and TIMP-1), because these enzymes participate in the degradation of the extracellular matrix including the basement membrane. Tumorous and adjacent nontumorous liver samples were obtained from 23 HCC patients who underwent a partial hepatectomy. In 16 of the 23 HCC samples, transcripts for MMP-9 were detected in the tumorous tissues, and 15 of 16 of these samples showed stronger expression in the tumorous tissues than in the nontumorous tissues. On the other hand, MMP-2 messenger RNA (mRNA) was detected in 18 of the 23 cases. Eight of these 18 cases showed more intense expression in the tumorous tissues than in the nontumorous tissues, whereas the expression levels were lower in the tumorous tissues than in the nontumorous tissues in 7 of 18 samples. With respect to the correlation between the clinicopathological features and mRNAs expression, it was found that the expression of MMP-9 mRNA in HCC with capsular infiltration was significantly higher than in HCC without capsular infiltration. HCC with capsular infiltration also tended to have a higher ratio of MMP-9 mRNA expression to TIMP-1 mRNA expression. In addition, the expression of MMP-2 mRNA in nontumorous cirrhotic tissues was significantly higher than in nontumorous tissues from patients with chronic hepatitis. Immunohistochemical examinations revealed that MMP-9 immunoreactivity was the most intense in the HCC cells, particularly in those cells in the marginal areas of the tumorous tissues. In conclusion, the present study shows that MMP-9 is closely participated in capsular infiltration in HCC.