The adsorption isotherms of four acid dyes on nylon 6 and deaminated nylon 6 fibers which differ in the drawing ratio by 2.0 or 5.0 have been determined at 90$^{circ}C$. The acid dyes used are C.I. Acid Orange 7, Blue 43 (monobasic), Blue 45 (dibasic), and Red 27(tribasic). Amino end group contents of nylon 6 and deaminated nylon 6 fibers are 5.9 ${ imes}$10-5 mole and 2.1 ${ imes}$10-5 mole per gram of fiber respectively. From the adsorption isotherms the equivalent saturation values of Orange 7, Blue 45, and Red 27 were nearly equal to the number of amino end group of fibers for nylon 6, but the values of di-and tribasic dyes were larger than the number of amino end group of fibers for deaminated nylon 6. There is a little reduction in the saturation values of four dyes as the draw ratio increase from 2.0 to 5.0 for both nylon 6 and deaminated nylon 6 fibers. The saturation value of Blue 43, a dye of low affinity, was smaller than the number of amino end group of fibers, i.e., the deviation from the stoichiometric adsorption incrased with the decrease in the affinity of dye.