The aim of this research is to investigate conditions for the removal of manganese ions from artificial groundwater by oxidation with KMnO4 to keep their concentration below the allowed levels (0.05 mg/L). The process includes low-level aeration and KMnO4 combination in a Jar test system. The manganese oxide (MnO2) particles produced from oxidation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The particles were in amorphous phase and were active adsorption sites for the removal of manganese ions. Parameters in the oxidation were solution pH, oxidant dosage, and stirring speed. The optimum solution pH was 8.0 which gave a complete Mn removal within 15 min. An increase of stirring speed diminished the rate of oxygen transfer and the proper speed was 120 rpm. Conversely, the adsorption activity of the particles at pH 9.0 complemented the oxidation of manganese ions exhibiting analogous effect with less consumption of KMnO4 than the required theoretical amount to complete the reaction.