Semiconductor sensors based on nanocrystalline SnO{sub 2}, In{sub 2}O{sub 3} and In{sub 2}O{sub 3}-SnO{sub 2} thin films have been investigated for detecting low concentration (2-20 ppm) of nitrogen dioxide in dry air. In this work the gas-sensitive layers were prepared by modified sol-gel methods making use of non-standard precursors and a suitable surfactant. The samples have been structurally and morphologically characterized by X-ray diffraction and SEM, respectively. Good gas-sensing responses towards NO{sub 2} have been found for all the prepared samples with improved performances for the In{sub 2}O{sub 3}-SnO{sub 2} based sensor. The performances of the sensors have been discussed according to the surface chemical reactions between the gas phase and the semiconductor.