Affinity and kinetic analyses for the evaluation of lectin-reactive α-fetoprotein (AFP) were performed using a biosensor based on surface plasmon resonance (SPR). Human AFP, purified from HCC (hepatocellular carcinoma) patients, was immobilized on the surface of a sensor chip. The interaction of this bound AFP with three lectins, Lens culinaris agglutinin [LCA], concanavalin A [Con-A] and erythroagglutinating phytohemagglutinin [E-PHA]) were monitored in real-time with the change in the SPR response. These three lectins produced an increase in the SPR response, indicating that all three bound specifically to the immobilized AFP. The association (k a s s ) and the dissociation (k d i s s ) rate constants clearly differed among the three lectin-AFP interactions. These affinity and kinetic analyses of the sugar binding specificities of lectins, employing a biosensor based on SPR, are expected to serve as a new technique with the potential for simple rapid evaluation of lectin-reactive AFP.