Removal of arsenic from water is significantly needed to supply safe drinking water worldwide. Here, a new and superior polymer of aminated poly(glycidyl methacrylate) (poly(GMA)-Am) adsorbents was fabricated and examined for effective removal of arsenic from water. The major result was that the arsenic adsorption of the poly(GMA)-Am adsorbents was greatly affected by the degree of amine of amination reagents. The poly(GMA)-Am-DETA fabricated by DETA reagent showed the highest arsenic adsorption efficiency, which was superior to two commercial anion exchange resins. A fast kinetic adsorption of arsenic by the poly(GMA)-Am-DETA was obtained within 1 h. The maximum adsorption capacity of the poly(GMA)-Am-DETA calculated by the Langmuir isotherm for As(V) and As(III) was found to be 78.7 and 13.5 mg/g, respectively. The Dubinin–Radushkevich model showed the arsenic adsorption on poly(GMA)-Am-DETA was governed by physical interaction, possibly due to its possessing a high density of ammonium functional groups covalent bonding to the polymer matrix. Regeneration of the poly(GMA)-Am-DETA exhibited no deterioration of the arsenic adsorption efficiency up to five cycles, where the desorption can be simply achieved with 0.1 M HCl solution. These results suggest a high potential of the reusable poly(GMA)-Am-DETA for effective removal of arsenic from drinking water.