In this study, we have synthesized TiO2 nanorods (NRs) on silicon and porous silicon (PS) substrates by hydrothermal method. The PS substrates with different porosities were fabricated by electrochemical anodization on silicon. According to the field emission electron microscopy images, TiO2 NRs grown on PS substrates have a better growth compared to those grown on silicon. Also increasing substrate porosity leads to an increase in density of the NRs. Atomic force microscopy observation demonstrates that porous layer formation due to etching of silicon surface leads to an increase of its roughness. Results indicate surface roughness evolution with porosity increasing enhances TiO2 nucleation on substrate and thus increases TiO2 NRs density. We propose a growth mechanism to explain how we can control the local surface chemical potential and thus the nucleation and alignment of TiO2 NRs by surface roughness variation. Also, photoluminescence studies show a red-shift in band gap energy of NRs compared to that of common bulk TiO2. (C) 2016 Elsevier B.V. All rights reserved.