This study focuses on the preparation of nano-NiO particles and their applications as catalysts in biomass pyrolysis. First, nano-NiO particles were prepared via precursors, which were obtained by homogeneous precipitation involving an aqueous solution of nickel nitrate hexahydrate and urea. Different approaches such as TGA, FTIR, XRD, BET, and TEM were used to characterize the precursors and nano-NiO particles. The formula of the precursor was identified as NiCO3 center dot 2Ni(OH)(2)center dot nH(2)O, and it could completely translate into NiO nanoparticles below 360 degrees C under an air atmosphere. The prepared nano-NiO particles were found to be spherical in shape and well dispersed with weak agglomeration. They had generally a high purity and fine crystal phase of cubic syngony with a mean size of similar to 7.5 nm and specific surface area of 188.0 m(2)/g. Furthermore, the catalytic activity of nano-NiO particles in pyrolyzing three biomass components (cellulose, xylan, and lignin) was preliminarily investigated using a thermogravimetric analyzer, and the results were compared with those of micro-NiO particles under the same conditions. With the presence of a catalyst, the weight loss of three biomass components mainly occurred at relatively lower temperature, with the final yield of residues and the activation energy of biomass pyrolysis being reduced markedly. Nano-NiO particles demonstrated a more effective catalytic effect in biomass pyrolysis over micro-NiO particles. The pathway of biomass pyrolysis in the presence of catalyst was briefly discussed.