CdS nanoparticles have been successfully synthesized by using DNA networks as templates. The synthesis was carried out by first dropping a mixture of cadmium acetate and DNA on a mica surface for the formation of the DNA network template and then transferring the sample into a heated thiourea solution. The Cd(2+) reacted with thiourea at high temperature and formed CdS nanoparticles on the DNA network template. UV-vis spectroscopy, photoluminescence, x-ray diffraction and atomic force microscopy (AFM) were used to characterize the CdS nanoparticles in detail. AFM results showed that the resulted CdS nanoparticles were directly aligned on the DNA network templates and that the synthesis and assembly of CdS nanoparticles was realized in one step. CdS nanoparticles fabricated with this method were smaller than those directly synthesized in a thiourea solution and were uniformly aligned on the DNA networks. By adjusting the density of the DNA networks and the concentration of Cd(2+), the size and density of the CdS nanoparticles could be effectively controlled and CdS nanoparticles could grow along the DNA chains into nanowires. The possible growth mechanism has also been discussed in detail.