Hexagonal cobalt hydroxide (beta-Co(OH)(2)) nanosheets over a size range from 100 nm to 1 mu m were synthesized using a very simple hydrothermal route with cobalt naphthenate as the cobalt source. Additionally, hexagonal cobalt oxide (Co3O4) nanorings over a size range from 100 nm to 1 mu m consisting of cubic nanocrystals were obtained via a hydrothermal method using as-prepared beta-Co(OH)(2) nanosheets as the precursors. A probable mechanism of formation of the hexagonal Co3O4 nanorings is proposed on the basis of time-dependent experimental results. (C) 2011 Elsevier Ltd. All rights reserved.