One-Dimensional (1D) MoS-decorated TiO nanotubes were synthesized by the anodization of TiO nanotubes followed by a hydrothermal process for MoS-decoration. The structure, morphology and surface characteristics of the MoS-TiO composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET). The results showed that TiO nanotubes can be filled and covered by flake-like MoS nanostructure. The numbers of the MoS layers ranged from 1 to 3. The TiO nanotube sensor shows a normal n-type response to reducing ethanol gas, whereas MoS-TiO exhibits p-type response with excellent sensing performances. Specially, the sensitivity for the MoS-TiO heterojunction increased almost 11 times than TiO nanotubes. This conversion of sensing behavior can be explained by the formation of p-n heterojunction structures.