We conducted previous research to apply several halochromic dyes to wool or nylon woven fabrics for the development of a textile chemosensor that can detect acidic solutions. In this study, we investigated the dyeing and acid-sensing properties of tropaeolin OO, a pH-indicating dye, on wool or nylon 66 woven fabrics. The maximum absorption wavelength of tropaeolin OO in an aqueous solution was found to be 440-450 nm with a light orange color in the pH range of 4 to 12. At pH 0.5 and 1, the maximum absorption wavelength shifted to 530 nm, resulting in a purple color. Between pH 1.5 and 3, the absorption curves showed an intermediate shape with a mixture of colors, ranging from red to orange. The color yields (K/S) of the dyed wool fabric were highly dependent on the dyebath pH and the dye concentration. The nylon fabric showed lower K/S values than the wool but exhibited good color yield. When the control sample dyed at pH 4 and a dye concentration of 1% o.w.f, was immersed in acidic solutions ranging from pH 1.5 to 5, no significant color changes were observed above pH 2.5. However, at pH 2 or below, the original orange color changed remarkably to dark purple or brown for wool and brown for nylon fabric. Neutralization of the discolored samples led to a complete recovery of the original orange color, indicating the possibility of repeated sensing. The dyed wool fabric showed moderate wash fastness and good rubbing fastness, while the nylon fabric exhibited good wash fastness and excellent rubbing fastness properties. These results suggest the potential application of both fabrics as acid-detecting textile sensors.