The serum heparanase level of 92 patients with hepatocellular carcinoma (HCC) measured by enzyme-linked immunosorbent assay (median, 91.4 U/mL) was higher than that of 19 healthy control subjects. Serum heparanase levels were higher in patients with HCC characterized by large tumors (>5 cm), advanced pTNM stage (III and IV), tumor capsule absence, and portal vein invasion. Positive correlations between serum heparanase and tumor heparanase expression were observed in 92 patients with HCC, 53 among them treated with tumor resection. In these 53 patients, the rate of microscopic venous invasion was significantly higher in 18 cases with high serum heparanase levels (>91.4 U/mL) than in the other 35 cases with low heparanase levels (14/18 vs 10/35; P = .001). Serum heparanase and vascular endothelial growth factor were identified as independent predictive factors for HCC microscopic venous invasion. The postoperative recurrence-free time (median, 8.7 months; range, 4.1-22.9 months), recurrence rate (72% [13/18]), 1.5-year disease-free survival rate (29.7%) were significantly worse in these 18 patients.