In this paper we report the structure and magnetic properties of flower-like alpha-NiS nanostructure prepared by a facile one-step hydrothermal method. The flowers consist of polycrystalline nanoflakes, and the nanoflakes are composed of single crystalline nanocrystals with an average size of about 15 nm. The alpha-NiS flowers exhibit the transition from paramagnetism to ferromagnetism with the blocking temperature of about 12 K. The field dependences of the magnetization prove that these flowers demonstrate a coexistence of antiferromagnetism and ferromagnetism at 5K, and exhibit a strong paramagnetic response at temperature higher than 100 K. (C) 2010 Elsevier B.V. All rights reserved.