Tremelliform Co0.85Se nanosheets have been successfully synthesized through a hydrothermal reaction of Co(NO3)(2)center dot 6H(2)O, Na2SeO3 and N2H4 center dot H2O without using any surfactant or structure-directing agents. The hydrothermal reaction products were confirmed as pure phase of Co0.85Se. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations further showed that the obtained products were flexible tremelliform nanosheets, which were composed of the slices with thickness of ca. 10 nm. Additionally, detailed investigation indicated that the formation of the tremelliform Co0.85Se nanosheets was strongly dependent on the reaction temperature, reaction time and reactant ratios. The obtained tremeliform Co0.85Se nanosheets displayed ferromagnetic properties at room temperature according to the magnetic measurement. More interesting, the as-prepared Co0.85Se nanosheets showed efficient catalytic performance for decomposition of hydrazine hydrate at room temperature. In addition, the stability and reversibility of Co0.85Se nanosheets as catalysts are also excellent, indicating that these nanomaterials can be used as long term catalysts in wastewater treatment. (C) 2012 Elsevier B.V. All rights reserved.