A new atomic layer deposition (ALD) process for nanocrystalline tin dioxide films is developed and applied for the coating of nanostructured materials. This approach, which is adapted from non-hydrolytic sol-gel chemistry, permits the deposition of SnO2 at temperatures as low as 75 °C. It allows the coating of the inner and outer surface of multiwalled carbon nanotubes with a highly conformal film of controllable thickness. The ALD-coated tubes are investigated as active components in gas-sensor devices. Due to the formation of a p-n heterojunction between the highly conductive support and the SnO2 thin film an enhancement of the gas sensing response is observed.