Nano-meter-sized silver iodide (n-AgI) powders were prepared by precipitation method at room temperature. The size, structure and specific surface area of the n-AgI powders were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscope and Brunner-Emmett-Teller, respectively. The n-AgI powders obtained have an average particle size of similar to 90 nm, similar surface lattice structure with ice crystal (H(2)O) and larger specific surface area than conventional micro-meter-sized silver iodide (m-AgI) powders. The cloud chamber experiment revealed that the n-AgI powders exhibit higher ice nucleation efficiency and higher threshold temperature value than conventional m-AgI powders. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.