A simple and flexiable route is presented to fabricate ordered micro/nanostructured porous films, based on a monolayer colloidal crystal template and solution dipping. In2O3 is chosen as a main model material to demonstrate the validity of the given fabrication strategy. It has been shown that the porous films with different microstructures, can be constructed directly on any desired substrate (with flat, curved, or even rough surface). The separately tunable sensitivity and response time in a large range and the gas sensing performances with both high sensitivity and fast response have been obtained only by controlling microstructures of the porous films. High stability, good reproducibility, and selectivity of the sensing performance have been achieved. Further, micro/nanostructured porous film sensors with desired sensing performances are designed and fabricated. This work could be important towards practical applications of micro/nanostructured porous-film-based sensors in the near future.