In this work, a new [Ag-Ag2O]/SiO2 nanocomposite material was prepared using 3-aminopropyltrimethoxysilane (AMPTS) as a connected material to absorb Ag-Ag2O nanoparticles on SiO2 surface. The [Ag-Ag2O]/SiO2 nanocomposite material had large surface, excellent conductivity and well redox activity. Then, a label-free immunosensor was prepared by the employment of the novel [Ag-Ag2O]/SiO2 nanocomposite material for determination of carcinoembryonic antigen (CEA). And the fabrication process of immunosensor was investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The [Ag-Ag2O]/SiO2 nanocomposite material could not only construct a desirable nano-sized surface with large surface-to-volume ratio to immobilize anti-CEA with the cooperation of nano-Au but also act as redox probe for the determination of CEA. By optimization of assay conditions on the pH of HAc-NaAc buffer, temperature and incubation time, the proposed electrode was proven to be sensitive and specific to detect CEA in the range of 0.5 to 160 ng/mL with a detection limit of 0.14 ng/mL, which was well within the normal physiological range. Additionally, the capability of the proposed immunosensor for direct CEA quantification in human blood serum was also discussed here. (C) 2010 Elsevier B.V. All rights reserved.