Nanoporous activated garlic stem carbon (AGSC) was prepared from garlic stem waste and used to remove As(III)from synthetic water under complete batch experiments. Characterization studies of AGSC were performed by FTIR, SEM, EDX, BET, XPS and XRD techniques. Batch adsorption experiments were carried out to study the adsorption of As(III) onto AGSC. Maximum removal of 93.3% of As(III) was obtained at optimum condition of pH 6, the adsorbent dose 5 g/L, equilibrium time 150 min, initial As(III) concentration 400 μg/L and temperature 298 K. Both Langmuir and Temkin isotherm model fitted well to the experimental data as compared to Freundlich isotherm. Kinetics indicated that the adsorption of As(III) was more suitable for pseudo-second-order than pseudo-first-order and Elovich model. The mass transfer mechanism could be described by Weber-Morris and Boyd mass transfer model. The maximum adsorption capacity of AGSC for As(III) removal was found to be 192.30 μg/g. The negative enthalpy and free energy change indicated that the adsorption process of As(III) onto AGSC was exothermic and spontaneous. The negative value of entropy change suggested decreasing randomness at the AGSC-aqueous As(III) interface during As(III) adsorption.