A synthesis of beta-Co(OH)(2) nanocrystalline materials has been investigated with the assistance of chelating agent ethylenedlamine. By controlling precipitation processes, various forms of beta-Co(OH)(2) crystallites can be prepared at different stages. The crystallite morphologies include two-dimensional hexagonal sheet platelets, one-dimensional nanorods, and butterfly-like nanocrystallite intermediates. In particular, a triangular construction unit for beta-Co(OH)(2) crystallites has been revealed with the ethylenediamine mediation in the synthesis. With the successful arrest of these butterfly-like intermediate crystallites, especially of linearly aligned "butterflies", the formation mechanism of one-dimensional nanorods or nanoribbons has been experimentally explained. The chemical composition of solution precursors and resultant beta-Co(OH)(2) crystallites has been analyzed with UV-vis/FFIR/CHN /XRD/TGA/TEM/SAED methods. The relationships among various observed crystallite morphologies have also been discussed on the basis of the experimental findings.