The degradation of rhodamine B (RB) in aqueous solution by Fenton’s reagent was studied. After 30 min, the 96.2% removal of RB in water (pH = 3.0, T = 25 °C) was achieved when the initial concentrations of Fe2+, H2O2 and RB were 0.5 mM, 5 mM and 10 mg/L, respectively. A higher initial concentration of Fe2+ and H2O2 resulted in a higher efficiency in RB discolorization. The removal of RB was dependent strongly on the pH value of solution. Increasing the reaction temperature was beneficial for the RB degradation. Based on the Arrhenius equation, the activation energy (Ea) was calculated to be 16.78 kJ/mol from rate constants at different temperatures. The degradation of RB by Fenton’s reagent was inhibited by the presence of oxalic acid.