Strong acids, such as hydrochloric acid and sulfuric acid, are colorless and difficult to detect when leaked by accident. A chemosensor using a halochromic dye can serve as a simple and easy detection method by exhibiting different colors when exposed to acidic liquids. In this study, bromocresol purple was used as a pH-indicating dye for detecting acidic liquids. Nylon 66 woven fabric was dyed with bromocresol purple, and the dyeing properties were investigated. The pH-sensing property was also investigated by dipping the dyed nylon fabric in an acidic solution. Bromocresol purple in an aqueous solution showed maximum absorption at 433 nm with a yellow color at pH 2-4, and at 589 nm with a blue color at pH above 6. The color yield (K/S) of bromocresol purple on nylon 66 is highly dependent on the dyebath pH. When the yellow sample, which was dyed at pH 3 or less, was immersed in a solution with pH 2-3.5, its original orange color was maintained. Then, the color turned blue when immersed in a solution with pH 4-5.5. In contrast, olive or olive green samples were obtained when dyed at pH 4-6. When the sample was immersed in a solution with pH 2-3.5, the color changed to yellow. The color also changed to blue when the sample was dipped in a solution with pH 4-5.5. The wash fastness of the fabric dyed at pH 3-5 ranged from very good to excellent.