The aim of this study is to investigate the conditions for the removal of manganese ions from synthetic groundwater by oxidation using KMnO4 to keep the concentration below the allowed level (0.05 mg/L). The process includes low-level aeration and addition of KMnO4 in a Jar test system with Mn2 + concentration of 0.50 mg/L, similar to that of natural groundwater in Taiwan. Different parameters such us aeration-pH, oxidant dose, and stirring speed were studied. Aeration alone was not sufficient to remove Mn2 + ions completely even when the pH was increased. When a stoichiometric amount of KMnO4 (0.96 mg/L) was used, a complete Mn2 + removal was achieved within 15 min at an optimum pH of 8.0. As the amount of KMnO4 was doubled, lower removal efficiency was obtained because the oxidant also generated manganese ions. The removal of Mn2 + ions could be completed at pH 9.0 using an oxidant dose of 0.48 mg/L because Mn2 + could be sorbed onto the MnO2 particles. Finally, The MnO2 particles were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).