Ag/SiO2 monolithic mesoporous nanocomposite was prepared by a simple impregnation of the preformed monolithic porous host in silver nitrate aqueous solution followed by ultrasonic irradiation of the liquid-solid mixture at room temperature. The formation and size of the particle in porous host have been determined from high-resolution transmission electron microscope (HRTEM), UV-Vis absorption band, and transmission electronic microscopy (TEM) analyses. It is found, due to the pore size limitation of mesoporous solid, the metal particles incorporated in have smaller size and more narrow size distribution than those formed simultaneously in corresponding soaking solution, and are located in the pores less than 10 nm in diameter. The proposed mechanism of noble metal nanoparticles formed within pores of mesoporous silica is discussed. It is assumed that the long-lived carriers of reducing power caused by the acoustic cavitation at the surface or near surface of porous monoliths is believed to play a major role in this pore doping processing. (C) 003 Published by Elsevier Science B.V.