Generation of X-ray induced secondary electrons in Ti and TiO2 was studied from both experimental and theoretical approaches, using X-ray photoclectron spectroscopy (XPS) attached to a synchrotron radiation facility and Monte Carlo simulation, respectively. The experiment revealed that the yields of secondary electrons induced by X-rays (electrons/photon) at photon energies to 4950 and 5000 eV for Ti and TiO2 are delta(Ti)(4950 eV) = 0.002 and delta(Ti)(5000 eV) = 0.014 while those for TiO2 are delta(TiO2)(4950 eV) = 0.003 and delta(TiO2)(5000 eV) = 0.018. A novel approach to obtain the escape depth of secondary electrons has been proposed and applied to Ti and TiO2. The approach agreed very well with the experimental data reported so far. The Monte Carlo simulation predicted; delta(*)(Ti)(4950 eV) = 0.002 and delta(*)(Ti)(5000 eV) = 0.011 while delta(*)(TiO2)(4950 eV) = 0. 003 and delta(*)(TiO2)(5000eV) = 0.015. An experimental examination on the contribution of X-ray induced secondary electrons to photocatalysis in TiO2 has also been proposed. (c) 2005 Elsevier B.V. All rights reserved.