A new nano-sized cobalt(II) coordination polymer, (CoL1).0.5DMF.1.5CH3OH(1); [H2L1 = 5-(4-Carboxy phenyl azo) salicyilic acid] has been synthesized by a sonochemical method. The thermal stability of compound 1 was studied by thermo- gravimetric and differential thermal analyses. Nano-structure of this coordination polymer was characterized by elemental analyses, IR spectroscopy,  powder X-ray diffraction and scanning electron microscopy. Nano-particles of Co3O4 were obtained by calcination of compound 1 at 550°C. The Co3O4  nano-particles were characterized by powder X-ray diffraction and scanning electron microscopy.