The simple and easy certain immobilization method for cell-adhesive protein onto titanium using tresyl chloride (2,2,2-trifluoroethanesulfonyl chloride) was developed. Tresyl chloride, which was liquid compound, was directly applied onto titanium at 37°C for 2 days. Then, tresylated titanium was immersed into the cell adhesive protein solution. Cell adhesive protein was immobilized onto titanium. Quartz-crystal microbalance technique and molecular orbital calculation for model compound revealed the effectiveness of tresyl chloride-activated technique. Initial cell attachment on cell adhesive protein immobilized titanium also showed the usefulness of tresyl chloride-activated technique. Tresyl chloride-activated technique will be applied to three-dimensional scaffold such as titanium fiber mesh ed for regenerative medicine.