© 2015 American Vacuum Society. Chemoresistive sensors based on multiwalled carbon nanotubes (MWCNTs) functionalized with SnO2nanocrystals (NCs) have great potential for detecting trace gases at low concentrations (single ppm levels) at room temperature, because the SnO2nanocrystals act as active sites for the chemisorption of gas molecules, and carbon nanotubes (CNTs) act as an excellent current carrying platform, allowing the adsorption of gas on SnO2to modulate the resistance of the CNTs. However, uniform conjugation of SnO2NCs with MWCNTs is challenging. An effective atomic layer deposition based approach to functionalize the surface of MWCNTs with SnO2NCs, resulting in a novel CH4sensor with 10ppm sensitivity, is presented in this paper. Scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy, and Raman spectroscopy were implemented to study the morphology, elemental composition, and the crystal quality of SnO2functionalized MWCNTs. High resolution TEM images showed that the crystal quality of the functionalizing SnO2NCs was of high quality with clear lattice fringes and the dimension almost three times smaller than shown thus far in literature. A lift-off based photolithography technique comprising bilayer photoresists was optimized to fabricate SnO2functionalized MWCNTs-based chemoresistor sensor, which at room temperature can reliably sense below 10ppm of CH4in air. Such low level gas sensitivity, with significant reversible relative resistance change, is believed to be the direct result of the successful functionalization of the MWCNT surface by SnO2NCs.