In the ultrasonic field,stable silver colloids were produced by the reduction of AgNO3 with the protection of PVP using KBH4 or N2H4.H2O as reductant.The main factors affecting the morphology of silver nanoparticles,such as distribution of the ultrasonic field,ultrasonic time,ultrasonic power,and the species of reductant,were studied.The silver colloids were identified by TEM and spectrophotometry.The results indicate that the factors such as distribution of the ultrasonic field,ultrasonic time,ultrasonic power,and the species of reductant have a great impact on the morphology of the silver nanoparticles.The size of the silver nanoparticles decreases with the ultrasonic power and ultrasonic time increasing.Ag nanoparticles prepared in standing wave field preferentially grow in a certain direction,which is propitious for forming hexagonal- and spherical-like silver nanoparticles.Monodispersed spherical silver nanoparticles are easily synthesized in the diffusion field.The stability of silver colloid becomes improved by ultrasonic treatment.For example,precipitate is not found after several weeks for the silver colloid prepared with an ultrasonic treatment time of 180 min.The silver nanoparticles prepared without ultrasonic treatment are large spherical-like and hexagonal.Well-dispersed spherical silver particles with a mean size of about 20 nm have been prepared under ultrasonic treatment.Spherical,spherical-like,and hexagonal silver nanoparticles can be obtained by changing the reductants..