The role of surface morphology of MoO3-doped SnO2 thin film on the gas sensing properties is analyzed. SnO2 thin films doped with 1, 3, 5 and 10 wt% MoO3 are prepared by sol-gel spin coating process. Structural and morphological properties are studied using glancing angle X-ray diffractometer, atomic force microscopy, transmission electron microscopy and high resolution transmission electron microscopy. Energy dispersive X-ray analysis and X-ray photoelectron spectroscopy studies are used for chemical analysis. A good correlation is found between the characteristics of the surface and gas sensing properties of these films. MoO3 addition is found responsible for increase in acidic nature of films which in turn increases their sensitivity and selectivity towards NO2 gas. (C) 2009 Elsevier B.V. All rights reserved.