Thin films of titanium dioxide with thickness of about 150 nm were deposited by spin coating method on a sapphire substrate from a sol-gel and annealed at various temperatures (from 600 degrees C to 1000 degrees C). Structural, optical and hydrogen gas sensing properties of the films were investigated. The annealing temperatures from 600 to 800 degrees C led to anatase phase with grain size in the range of 14-28 nm. Further increase of the annealing temperature resulted in transformation to rutile phase with larger grain size of about 100-120 nm. The optical band gap tended to decrease with increasing annealing temperature. The estimated values of activation energy for charge transport were in the range of 0.6-1.0 eV for films annealed at temperatures from 600 degrees C to 800 degrees C and 0.37-0.38 eV for films annealed at 900 degrees C and 1000 degrees C. The films annealed at 900 degrees C and 1000 degrees C showed better hydrogen sensitivity, what can be at least partially caused by their higher surface roughness. (C) 2012 Elsevier B. V. All rights reserved.