The Ag nanorods and nanofibers have been synthesized in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/ isooctane reverse micelles with the aid of low-intensity ultrasonication. The TEM results show that only spherical silver nanoparticles can be obtained from the reverse micelles in the absence of ultrasonication whereas needle-shaped and wire-shaped silver particles are obtained as ultrasonication is applied. The possibility of ultrasonication to induce the aggregation of nanoparticles dispersed in reverse micelles is also confirmed by UV spectra. Small-angle X-ray scattering (SAXS) is used to obtain information on the microstructure change of the reverse micelles by ultrasonication. It is revealed that by ultrasonication the micelles change from a spherical to an ellipsoidal structure, of which the size can be tuned by the ultrasonication time.