Tissue factor pathway inhibitor (TFPI) is a heparin-binding protein involved in the extrinsic blood coagulation system. In order to elucidate the minimal size of heparin chain required for the interaction with TFPI, we prepared a series of heparin-derived oligosaccharides with tailored chain length ranged from disaccharide to eicosasaccharide after the successive treatments of heparin, including partial N-desulphation, deaminative cleavage with nitrous acid and gel-filtration. Affinity chromatography study of each oligosaccharide fraction using TFPI as the ligand indicated that increasing the degree of polymerisation causes increased affinity, and that a remarkable change in the affinity occurs between the decamers and dodecamers. Measurement of factor Xa inhibitory activity of TFPI in the presence of each oligosaccharide fraction indicated that the fractions shorter than dodecamers only slightly enhanced the TFPI activity for factor Xa inhibition, while the fractions larger than octadecamers had an effect comparable to full-length heparin. These were compatible to the results from the kinetic analyses of the interaction between TFPI and heparin-derived oligosaccharide with an evanescent wave-based biosensor system, IAsys, using a TFPI C-terminal peptide as the ligand.