A new method was established to construct a ultrasensitive electrochemiluminescence (ECL) immunosensor by using Ru@SiO2 (Ru(bpy)3 2+ doped silica) - doped Au (Ru@SiO2-Au) composite nanoparticles to label Ru-Ab2 (monoclonal α-fetoprotein (AFP) antibody labeled with Ru(bpy)32+). The primary antibody, anti-AFP was first immobilized on the multi-walled carbon nanotubes (MCNTs) modified with gold nanoparticles (MCNTs-Au) modified glassy carbon electrode due to the covalent conjugation, then the antigen and the Ru@SiO2-Au composite nanoparticles labeled Ru-Ab2 (Ru@SiO2-Au~Ru-Ab2)was conjugated successively to form a double-conjugated Ru(bpy)32+ sandwich-type immunocomplex through the specific interaction. Accordingly, through the ECL response of Ru@SiO2-Au~Ru-Ab2 and tripropylamine (TPA), a strong ECL signal was obtained and an amplification analysis of protein interaction was achieved. The present immunosensor performed high sensitivity and wide liner for detection α-fetoprotein (AFP) in the range of 0.05-80 ng mL−1 and the limit detection was 0.025 ng mL−1(defined as S/N=3). The morphologies of MCNTs, MCNTs-Au, Ru@SiO2 and Ru@SiO2-Au nanoparticles were characterized by using transmission electronic microscopy (TEM). The developed label and method is versatile, offers enhanced performances, and can be easily extended to other protein detection.