It is known that the "race for the surface" determining the in vivo response is strictly connected to the physico-chemical properties of the material, especially at its surface. Accordingly, the study of surface roughness, charge and wettability is fundamental to predict the bio-response to the implant. In this work, streaming potential was chosen as a reliable method to quantify the solid surface charge of hydrothermally treated (HT) TiO2-anatase nano-crystalline coatings, grown on titanium substrates. The influence of metal and ionic conductance on the zeta potential values was taken into account, allowing for the correlation of the surface charge with the coating porosity, the semiconductor character of the TiO2 nano-crystals and the metallic nature of the bulk titanium.