Heparin-modified hydroxyapatite (HAP-HP) particles were prepared by an in situ coprecipitation method and were characterized by Fourier transform infrared spectrometry, x-ray diffraction and transmission electron microscopy. The heparin content in the particles was determined by a colorimetric assay and energy dispersive x-ray spectroscopy. Final results indicated that the crystallinity and crystal size decreased as both the Ca/P molar ratio and sulfur content increased by adding heparin. Blood compatibility of the HAP-HP particles was evaluated by activated partial thrombin time and prothrombin time. The clotting time of HAP-HP was prolonged remarkably compared with that of HAP. Above all, this novel HAP-HP material can be potentially applied as compatible blood materials for drug carriers of intravenous injection and artificial blood vessels.