The adhesion of bone cells on substrate materials is generally measured by the removal torque and/or contact area between bone and implants. In this study, collagen was used as a surfacegrafting material on hydroxyapatite (HA) substrates to enhance the cell adhesion because the collagen is a major constituent of connective tissues and has been regarded as one of the most excellent coating materials for bone bonding. First, HA disks (10mmΦ x 1mm) were prepared and then collagen was immobilbized on the HA surface using an 3-APTES coupling agent to improve the adhesiveness of cells on HA disk surfaces. NIH 3T3 fibroblasts were seeded on the collagengrafted and non-grated HA disks and cultured in a Dulbecco’s modified eagle medium containing 10% fetal bovine serum for 3 hrs to evaluate the cell adhesion on the HA samples. The fibroblasts on the collagen-grafted sample were more spread than those on the non-grafted sample. It is believed that collagen-grafted HA surface provides suitable sites for cell attaching due to the high biocompatibility of collagen.