To increase the performance of silk fabrics, especially their dyeability, a cationic modifying agent, 3-(trimethoxysilyl) propyl dodecyl dimethyl ammonium chloride (HSQA), was prepared in our laboratory. The dye behavior of the cationized silk was examined with five leveling-type acid dyes. Better color shades and good washing fastness were achieved after silk was cationized by HSQA, and it was possible to dye silk under neutral conditions at 70 degrees C. The equilibrium adsorption isotherm and kinetic properties of the cationized silk dyed with CI Acid Orange 7 were investigated. The adsorption of Cl Acid Orange 7 onto the HSQA-cationized silk was also in good agreement with the Langmuir isotherm, with an enthalpy and an entropy of -20.13 kJ/mol and -30.06 J/mol K respectively. A pseudo-second-order kinetic model agreed well with the dynamic behaviors for the adsorption of Cl Acid Orange 7 onto the cationized silk under neutral conditions, with the activation energy decreasing from 61.87 to 53.32 kJ/mol. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 1005-1012, 2008.