Biofunctionalized magnetic nanoparticles (BMNs) that provide unique advantages have been extensively used to develop immunoassay methods. However, these developed magnetic methods have been used only for specific immunoassays and not in studies of magnetic characteristics of materials. In this study, a common vibration sample magnetometer (VSM) was used for the measurement of the hysteresis loop for different carcinoembryonic antigens (CEA) concentrations (Φ CEA) based on the synthesized BMNs with anti-CEA coating. Additionally, magnetic parameters such as magnetization (M), remanent magnetization (M R), saturation magnetization (M S), and normalized parameters (ΔM R/M R and ΔM S/M S) were studied. Here, ΔM R and ΔM s were defined as the difference between any Φ CEA and zero Φ CEA. The parameters M, ΔM R, and ΔM S increased with Φ CEA, and ΔM S showed the largest increase. Magnetic clusters produced by the conjugation of the BMNs to CEAs showed a ΔM S greater than that of BMNs. Furthermore, the relationship between ΔM S/M S and Φ CEA could be described by a characteristic logistic function, which was appropriate for assaying the amount of CEAs. This analytic ΔM S/M S and the BMNs used in general magnetic immunoassays can be used for upgrading the functions of the VSM and for studying the magnetic characteristics of materials.