ABSTRACT Acidochromic fluorescent membranes have garnered significant research interest owing to their potential in real‐time environmental monitoring and smart sensing applications. However, the rational design of membranes to optimize their structure–property interplay for enhanced acidochromic performance remains further explored. Herein, we prepared various stimulus‐responsive micro/nanofibrous membranes using electrospinning technology by incorporating a fluorescent small molecule (TPECNPy‐2) with thermoplastic polyurethane (TPU) to obtain specific properties. The effects of varying the TPECNPy‐2 content on the chemical–physical structure and acidochromic properties of the composite membranes were analyzed. The results indicated that the addition of TPECNPy‐2 had no significant impact on the chemical structure, fiber morphology, or aggregation state of the composite membranes. Morphology assessment revealed that the fabricated TPECNPy‐2/TPU composite membranes exhibited uniform fiber diameters of approximately 100 nm, demonstrating excellent spinnability and reproducibility, while FL analysis revealed that all composite fiber membranes exhibited reversible acidochromic behavior. Under acid vapor exposure, the maximum fluorescence emission wavelength shifted from 505–511 to 622–625 nm. After fumigation with triethylamine, the fluorescence emission returned to its initial state, and the membrane reverted to its original color under visible light.