The adsorption behavior of Eosin Y on activated carbon (AC) in batch system was investigated. The adsorption isotherm could be well fitted by the Langmuir adsorption equation. The kinetics of adsorption followed the pseudo-second-order model. The temperature variation was used to evaluate the values of free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°). The positive value of enthalpy change ΔH° for the process confirms the endothermic nature of the process and more favourable at higher temperature, the positive entropy of adsorption ΔS° reflects the affinity of the AC material toward Eosin Y and the negative free energy values ΔG° indicate that the adsorption process is spontaneous. With the increase of the amount of AC, removal efficiency of Eosin Y was increased, but adsorption capacity was decreased. And adsorption capacity was increased with the decrease of particle size. With the increase of the amount of AC, removal efficiency of Eosin Y was increased, but adsorption capacity was decreased. And adsorption capacity was increased with the decrease of particle size.