Recently, nitrogen-doped carbon materials have proved to be effective catalytic platforms for the oxygen reduction reaction (ORR). Despite the recent synthetic advances for the preparation of nitrogen-incorporated carbon materials, the low-temperature and water-based synthesis of nitrogen-doped carbon materials has rarely been explored due to the difficulties in nitrogen-doping under such mild conditions. Here, nitrogen-doped Pt/C (Pt/NC) catalysts are prepared using a facile, low-temperature, aqueous-phase method. Hydrazine treatment of a Pt/C catalyst successfully yields Pt/NC with controlled nitrogen content. The as-prepared Pt/NC catalysts exhibit enhanced electrocatalytic activity and stability toward ORR in comparison to nitrogen-free Pt/C, and their ORR activities are highly dependent on the level of nitrogen-doping. The Pt/NC catalyst containing 2.0 at % nitrogen results in the largest improvement of ORR activity.