CdS/PAM nanocomposites have been successfully synthesized in situ via a ultrasound- assisted route under ambient condition, employing CdCl2 and Na2S2O3 as Cd2+ and S2- ion sources and acrylamide (AM) and (NH4)(2)S2O8 as organic monomers and initiating reagents, respectively. The results from X- ray powder diffraction ( XRD) analysis and the IR spectrum of the final product showed the formation of CdS nanoparticles and the polymerization of AM monomers. SEM observations showed that the CdS/PAM nanocomposites could film on the quartz substrate and some holes in which many nanorods regularly arranged distributed on the film. The UV- vis absorption and PL spectra of CdS/PAM nanocomposites obviously differed from those of CdS nanoparticles prepared under the same conditions due to the presence of PAM. The electrochemical research showed that CdS/PAM nanocomposites had a stronger ability to promote electron transfers between Hb and the Au electrode than CdS nanoparticles prepared under the same conditions. A possible formation mechanism was also suggested based on the results of experiments.