Differently shaped zinc oxide nanostructures were synthesized at 90 degrees C by refluxing process at different refluxing times (6, 12, 18 and 24 h) via the solution method using zinc acetate dihydrate as a source material and hydrazine hydrate. Heterostructures like needle shaped nanorods, flowers composed with nanorods, pencil like zinc oxide nanorods and square shaped zinc oxide micro-particles were observed using field emission electron microscopy (FE-SEM) as functions of varying refluxing time of the solution of zinc acetate dihydrate (Zn(Ac)(2) 2H(2)O) and hydrazine hydrate (N(2)H(4) H(2)O). A high-resolution transmission electron microscopic (HR-TEM) observation supports FE-SEM observations and revealed that nanostructures grew along [0001] direction with an ideal lattice fringe distance of 0.52 nm, same as that of bulk ZnO. X-ray diffraction patterns present good crystalline properties and that the obtained powder is zinc oxide without any other impurities. The compositional study. FUR spectroscopic measurement showed a standard peak of zinc oxide at 518 cm(-1). In addition to this, we also proposed the chemical growth mechanism of different types of grown zinc oxide nanostructures. (C) 2010 Elsevier B.V. All rights reserved.