To improve the adsorption of perchlorate (ClO4-) in contaminated water, granular activated carbon (GAC) was modified with cetyltrimethyl ammonium chloride (CTAC). To investigate the adsorption mechanism of perchlorate the structure of GAC-CTAC was characterized by scanning electron microscopy (SEM) and FTIR spectroscopy. Then the GAC-CTAC was used for the adsorption of perchlorate in water. The effects of the adsorption time, pH, initial ClO4- concentration, and co-existed anions on perchlorate adsorbed by GAC-CTAC were studied. The results show that the GAC-CTAC could absorb perchlorate better in water. The adsorption capacity of perchlorate on GAC-CTAC decreases in the alkaline solution, and increases with increasing the initial concentration. The competitive adsorption exists between co-existed anions and ClO4- on GAC-CTAC. In addition, adsorption of ClO4- on GAC-CTAC fits the Langmuir, Freundlich and Tempkin isothermal models in the range of the experimental concentration. The adsorption process follows pseudo-second order kinetics.