The magnetic relaxation switches（MRS）technology based on superparamagnetic nanoparticles（SMP） and their applications in biochemical analysis were introduced in this paper.In homogenous magnetic field of miniaturized nuclear magnetic,the dispersed and aggregated states of SMP produce local inhomogeneities in the applied magnetic field,resulting in the decrease or increase in the spin ± spin relaxation time（T2） of surrounding water molecules,which is called magnetic relaxation time（MRS） sensing effect.The magnetic particles binding with specific molecules can act as magnetic relaxation switches（MRS） when they coupled specially with target analytes.In MRS assays,the presence of an analyte causes the particles to transition between dispersed and clustered states and affects the T2 relaxation times of surrounding water molecules.Compared with the conventional immunological methods,MRS assay is more sensitive,simple and time-saving due to its combination of nanobiotechnology,nuclear magnetic resonance and immunoassay.Predictably,it has a remarkable application potential in the fields of medical diagnosis,environmental monitoring,food safety analysis,public healthy security and molecular interactions study,etc.