Hyperbranched polyester-encapsulated crystals of silver nanoparticles with size in 3-19 nm, average 7.7 +/- 0.5 nm, were prepared by ultraviolet irradiation of silver ions with the assistance of hyperbranched polyesters terminated by -OH and -COOH groups and aliphatic phosphate surfactant. The silver nanoparticles were characterized by transmission electron microscopy, selected area electron diffraction, UV-vis spectra, X-ray diffraction, X-ray photoelectron spectra and Fourier transform infrared spectroscopy. Controlled and comparing experiments showed that non-aggregated silver nanoparticles could not be synthesized without the using of either hyperbranched polyester and aliphatic phosphate surfactant, indicating the importance of hyperbranched polyester and phosphate surfactant in stabilizing silver nanoparticles during the photoreduction. (c) 2005 Elsevier B.V. All rights reserved.