In this paper, nanosize metal Schiff base complexes M((nac)₂en)Cl₂, (nac)₂en = N,N′-bis(paranitroacetophenone)ethylenediamine, M = Hg (1), Co (2) and Mn (3), have been prepared by ultrasonic bath assisted and were characterized by elemental analyses (CHN) and SEM. The thermal behavior of the complexes from room temperature to 700 °C shows different weight losses. In addition, the complexes used as new precursors for preparation of metal oxide nanoparticles by solid-state thermal decomposition at 600 °C. Metal oxide nanoparticles were characterized by FT-IR, XRD and SEM.