Silver nanoparticles (AgNPs) are synthesized by chemical reduction method and characterized by UV-vis spectra, transmission electron microscopy, and high performance particle sizer. We have found that AgNPs could enhance the chemiluminescence (CL) intensity of luminol-H2O2 system. In this reaction, luminol intermediate is generated under alkaline condition on the surface of AgNPs in luminol-H2O2 system and enhances CL intensity. To validate the reaction mechanism, AgNPs are bound with thioglycolic acid (Ag-HSCH2COOH) and then joined to BSA protein (Ag-BSA). We investigate the CL intensity in the presence of Ag-HSCH2COOH or Ag-BSA comparing with that in the presence of AgNPs and conclude the catalytic reaction take place on the surface of AgNPs. (c) 2007 Elsevier Inc. All rights reserved.