Five different magnetic phase transitions have been identified and characterized in stoichiometric Nd 2 NiO 4 by means of magnetic-susceptibility and isothermal-magnetization measurements. A collinear antiferromagnetic ordering of Ni 2 + magnetic moments exists between T N 1 ≊320 K and T c 1 ≊130 K where an orthorhombic-to-tetragonal structural phase transition occurs. In this temperature range, Nd 3 + ions follow a simple paramagnetic Curie-Weiss-like behavior, while a weak ferromagnetic component appears below 130 K. An internal magnetic field on the Nd 3 + ions develops with this structural phase transition. Two additional transitions are observed at T c 2 ≊68 K and T c 3 ≊45 K which are characterized by a sudden increase of the weak ferromagnetic component. Finally, a peak of the differential susceptibility at T N 2 ≊11 K marks a long-range antiferromagnetic ordering of the Nd 3 + ions. The internal magnetic field acting on the Nd ions was evaluated to be 5.2 T in the 20 K– T c 2 temperature range.