The temperature and magnetic field dependent magnetization of the two-dimensional quantum spin system Ni-5(TeO3)(4)Cl-2 has been investigated using single crystals in temperature range 1.8-100 K and in magnetic fields up to 14 T. The magnetization below the magnetic phase transition demonstrates an unusual temperature behavior with considerable anisotropy. Combined magnetization and specific heat data allowed to determine the critical temperature of the magnetic phase transition, T-c = 28.4 K. Magnetic fields shift this temperature toward lower temperatures. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3674203]