This paper reports a simple method to prepare Ni/NiO powders containing nano- and micro-sized pores using ethylenediamine (EDA or en) as a chelating agent. Ni-ethylenediamine complexes were synthesized hydrothermally using nickel (II) nitrate as a Ni precursor and a bidentate chelating reagent, EDA, at various molar ratios (nickel precursor: EDA = 1.0:1.0 1.0:2.0,1.0:3.0, and 1.0:4.0). X-ray diffraction and scanning electron microscopy showed that the produced powders were Ni/NiO composites containing nano- and micro-pores with two distinct pore size ranges, 100-300 nm and 1.0-2.0 mu m. The adsorption-desorption isotherm curves revealed a certain hysteresis slope at intermediate and high relative pressures. This indicates the presence of large pores, which were shown by variations in the mean pore diameter (D-p); 6.57, 11.61, 12.41, and 15.478 nm for Nienl, Nien2, Nien3 and Nien4 corresponding to an EDA: Ni precursor molar ratio of 1.0, 2.0, 3.0 and 4.0, respectively. The specific surface areas and total pore volumes for the Nien1, Nien2, Nien3, and Nien4 were 20.4, 41.21, 50.60 and 27.64 m(2) g(-1), respectively. (C) 2013 Elsevier B.V. All rights reserved.