Herein we combine the enzyme-nanoprobe induced biomineralization of cupric subcarbonate with a sensitive copper chromogenic reaction to develop an ultrasensitive colorimetric immunosensing method. The nanoprobe was prepared through the surface assembly of signal antibody and high-content urease on the nanocarrier of gold nanoparticle (Au NP). Upon sandwich immunoreaction at a magnetic bead (MB)-based immunosensing platform, the analyte of carcinoembryonic antigen and the Au NP/urease nanoprobe were quantitatively captured onto the MB surface successively to form an immunocomplex. The enzyme reaction of the nanoprobe resulted in the catalyzed hydrolysis of the urea substrate to produce large amounts of OH⁻ and HCO₃⁻. These ions were further combined with added Cu²⁺ to form the biomineralization of cupric subcarbonate rapidly on the immunocomplex. Based on the acid-release of Cu²⁺ from the biomineralized products for the chromogenic reaction, a red complex was obtained and employed for the ultrasensitive colorimetric signal transduction. Under the optimum conditions, a linear range over five orders of magnitude was obtained with a low detection limit of 0.45 pg/mL. In addition, this method features low cost, rapid and convenient operation as well as satisfactory reproducibility, stability and accuracy. It thus owns great potentials for practical applications.