Nano-particles of a Ni(II) metal–organic framework (MOF) with cubic building blocks and 1D open channels, i.e. {[Na16(Ni8L12)(H2O)20(H3O)4](CH3CN)(H2O)18.5}∞ (1) (H3L=4,5-imidazoledicarboxylic acid) were synthesized by using ultrasonic method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), IR spectroscopy and elemental analysis. The effect of concentration of starting reagents on size and morphology of nano-structured compound 1 has also been investigated. Calcination of the bulk powder and nano-sized compound 1 at 700°C under air atmosphere yields NiO nano-particles. Results show that the size and morphology of the NiO nano-particles are dependent upon the particles size of compound 1.