In this study, amide and amine groups bound to poly(ethylene terephthalate) fibers are used to remove the colored toxic Congo red dye from aqueous solution. The effects of process variables like pH, contact time, graft yield, and initial dye concentration on the adsorption were investigated. The maximum adsorption of Congo red to amide and amine groups was observed at pH 3 and 5 respectively. Equilibrium was attained at approximately 60 min for the amine group. The adsorption capacity of amine group on the poly(ethylene terephthalate) fiber was 46.5 mg $g^{-1}$ at $25^{circ}C$, which was higher than that of the amide group on the poly(ethylene terephthalate) fiber. Desorption was done using 0.1 M $NH_3$, and recovery was measured at 58.2 %. The used adsorbent was regenerated and recycled six times. The results showed that the amine-functionalized fiber could be considered as potential adsorbents for removal of Congo red from aqueous solution.