Adsorption and desorption behaviors of human serum albumin (HSA) on titanium particles were examined as a function of pH. The HSA showed a high affinity-type isotherm with well-defined saturation values, even when HSA had a net charge that was the same type as that of titanium. The saturated amount of HSA adsorbed (Γ_sat) depended on pH. The maximum value of Γ_sat was obtained at pH around the apparent point of zero charge of HSA, where the net charge (Z_H⁺app) of HSA was zero and where HSA has the minimum intrinsic viscosity ([η]), reflecting the molecular volume. Results showed that the Z_H⁺app and [η] of HSA are the most important factors determining the Γ_sat value. Curves for the surface charge density (σ_app) of HSA-adsorbed titanium prepared at initial pH 7.4 showed that carboxyl groups on HSA contributed to interactions even with the negatively charged titanium surfaces. The possible interactions between ionic functional groups on HSA and titanium were discussed based on measurements of variation in pH of solutions, i.e., uptake or release of proton (ΔpH) as a result of adsorption. The removal of HSA from titanium surfaces was more rapid when using alkaline solutions, particularly at pH greater than 11. Results showed that HSA was adsorbed onto titanium surfaces, even under unfavorable electrostatic conditions, through various interactions between ionic groups on HSA and surface OH groups on titanium, the magnitude of those interactions was diminished by the OH⁻cleaning action.