The human enzyme heparanase has been shown to function in tumour progression, metastatic spread and tumour angiogenesis. The aim of the present study was to assess heparanase expression assessed by immunohistochemical staining (IHC) in endometrial cancer in correlation with clinicopathological factors. A total of 52 endometrial cancers were obtained from previously untreated patients (median age, 56 years, range, 35-80 years). The expression of heparanase was evaluated by using IHC with anti-heparanase polyclonal antibody. This antibody was raised by immunising a rabbit with a peptide containing the amino acid residues from 238 to 250 of the heparanase. The IHC data were used to determine the relationship between heparanase expression, and clinicopathological parameters. IHC showed that the heparanase was expressed in 23 of 52 (44.2%) endometrial cancers. Heparanase was abundantly and equally expressed in both the cytoplasm and the cell membrane of the cells in endometrial cancer. Strong heparanase-positive staining was also seen at the invasive front of the tumour into myometrium. The expression was significantly related to lymph-vascular space involvement (p = 0.0028), depth of myometrial invasion (p = 0.0026), and histological tumour grade (p = 0.0135). In six tumours with positive lymph nodes, the heparanase expression was observed as being higher compared with tumours with negative lymph nodes, which was not significant (p = 0.2349). In terms of peritoneal cytology, ovarian metastasis, and cervical invasion, we observed no significant difference in the heparanase expression assessed by IHC. These results suggest that the expression of heparanase may promote tumour invasion into myometrium and lymph vascular space in endometrial cancer.