Titanium dioxide (TiO2) is well applied in implant materials because of its biocompatibility while carbon is usually regarded as toxicant to cells. Actually, water-surface interaction has significant influence on the biocompatibility of implant materials. To understand the difference between TiO2 and graphite on the biocompatibility, molecular dynamics simulations were performed to study the structure and diffusion of water in nano-slits formed by rutile TiO2(1 1 0) and graphite(0 0 0 1) with the separation distance ranging from 0.8 to 2.0 nm. Simulation results show that the residence time of water at TiO2 surface is considerably longer than that at graphite surface, indicating the stronger interaction between water and TiO2. Moreover, the microstructure of water molecules absorbed at the TiO2 and graphite surfaces were analyzed; the bound water molecules at the TiO2 surface and the hydrogen bond network reduce the diffusivity of water through the TiO2 slits. Simulation results show that the surface chemistry is crucial to the diffusion of water in nanoscale pores, while geometric size effect may just enhance the chemical effect. (C) 2010 Elsevier B.V. All rights reserved.