Several studies have demonstrated that heparin can significantly inhibit the P-selectin-mediated interaction of platelets and tumor cells during metastasis as a P-selectin ligand. However, little information is available about the specific oligosaccharide structures of heparin in recognition by P-selectin. Two chemically modified heparins, CR-heparin and SCR-heparin were prepared, to explore if such heparin derivatives can reduce the P-selectin-mediated A375 tumor cell adhesion. The results indicated that CR-heparin with low anticoagulant activity could significantly inhibit the P-selectin-mediated A375 tumor cell adhesion, demonstrating that 6-carboxyl group of the glucuronic acid in heparin may not be crucial for recognizing by P-selectin. In contrast, SCR-heparin reduced the inhibiting activity dramatically, suggesting that the recognition of P-selectin to heparin depend on not only densities of negative charge. These results provide valuable experimental evidence for clarifying the molecular mechanism of P-selectin-mediated tumor cell adhesion.