In order to characterize electron traps in TiO2 nanoparticles, we performed time-resolved microwave photoconductance measurements at temperatures ranging from 93 to 373 K. It was found that the initial photoconductance was almost temperature independent, while the photoconductance decay was thermally activated. From the results it is inferred that on pulsed UV illumination, part of the conduction band electrons decay on a picosecond timescale by deep trapping or by recombination. Thermally activated interparticle hopping towards the bulk of the TiO2 film, results in deep trapping of remaining conduction band electrons, which explains the photo-conductance decay on the microsecond timescale. (C) 2008 Elsevier B.V. All rights reserved.