Interactions between antibody and antigen molecules play essential roles in biological recognition processes as well as medical diagnosis. Therefore, an understanding of the underlying mechanism of antibody–antigen interactions at the single molecular level would be beneficial. In the present study, human immunoglobulin (IgG) tethered cantilevers and rat anti-human IgG functionalized gold surfaces were fabricated by using selfassembled monolayers method. Dynamic force spectroscopy was employed to characterize the interactions between human (IgG) and rat anti-human IgG at the single-molecule level. The unbinding forces were determined to be 44.6 ±0.8, 65.8 ± 3.0, 108.1 ± 4.1, 131.1 ± 11.2, 149.5 ± 4.7, 239.5 ± 3.1 and 294.7 ± 7.7 pN with ramping loading rates of 514, 1,127, 3,058, 7,215, 15,286, 31,974 and 50,468 pN s-1, respectively. In addition, the unbinding forces were found to be increasing with the logarithm of apparent loading rates in a linear way. Fitting data group resulted in two distinct linear parts, suggesting there are two energy barriers. The corresponding distances in the bound and transition states (xb) and the dissociation rates (Koff) were calculated to be 0.129 ± 0.006 nm, 3.986 ±0.162 s-1 for the outer barrier and 0.034 ± 0.001 nm, 36.754 ± 0.084 s-1 for the inner barrier. Such findings hold promise of screening novel drugs and discerning different unbinding modes of biological molecules