Single-walled carbon nanotubes (SWNTs) have potential for creating high performance gas sensors, but the number of gases that can be detected is still limited and the sensitivity needs further improvement. Here, large-area SWNT films directly synthesized by chemical vapor deposition are configured into gas sensors for a range of toxic gases such as NH3, NO, and NO2. In particular, a SWNT-Fe2O3 composite film obtained via a simple annealing process produces a stable response to H2S and shows enhanced sensitivity to NO2 and at room temperature, compared with pristine SWNT films. Formation of uniform Fe2O3 nanoparticles throughout the porous film is responsible for improved performance and enabling sensing to more gases, and removes conventional steps such as chemical functionalization or doping. Flexible sensors that can be bent to large angles repeatedly are also demonstrated. SWNT films containing a large amount of residual catalyst can be directly manufactured into large-area, flexible or wearable, thin film or textile-configured sensors for various toxic gases.