A biotinylated anti-rat C-reactive protein (CRP) antibody was ingeniously prepared by the reaction of the unmodified antibody with a water-soluble sulfosuccinimidyl-6-(biotinamido)hexanoate. The molar biotin incorporation of the resulting modified antibody was found as 5.82. A flow-type indirect-competitive quartz crystal microbalance immunosensor system was constructed with the sensor chip immobilized with 2mg/mL CRP as the coating antigen. When 200μL of the modified antibody having the concentration of 0.250mg/mL was added with a streptavidin-coated gold nanoparticle (GNP) to the immunosensor system, the frequency shift obtained was 139.8±0.3Hz. Compared to the frequency shift of 91.1±1.3Hz found with the addition of the unmodified antibody only, the signal augmentation after GNP binding amounted to 53.4%, which resulted in sensitivity improvement of the current immunosensor.