The preparation and characterization of modified cotton fabrics with responsive pH was studied. The objective was to prepare the modified cotton fabric with pH sensitivity and evaluate the color change of the dyed cotton fabrics in acetic acid and urea solutions. The cotton fabric was cationized with diallyldimethylammonium chloride at room temperature by using potassium persulfate as an initiator, N,N '-methylenebisacrylamide as a cross-linker and N,N,N ',N '-tetramethylethylenediamine as an accelerator. The unmodified and modified cotton fabrics were dyed with a bromothymol blue at room temperature for 1h and the color in various solutions measured. It was found that the color on the dyed cotton fabrics responsed with the pH as the smart cotton fabrics. In addition, the addition of the N,N '-methylenebisacrylamide in the polymerization reaction caused the deep shade in comparison with no N,N '-methylenebisacrylamide. Factors affecting the color change of the dyed cotton fabric with the bromothymol blue were concentration of diallyldimethylammonium chloride, ionic capacity, concentration of N,N,N ',N '-tetramethylethylenediamine and type of solutions.