OBJECTIVE To detect 3-dimensional images of anti-N-methyl-D-aspartate receptor Nr1 (NMDAr1) polycolonal IgG affixed on mica in physiological environment. METHODS The images and data were obtained from a contact mode and commercial Si3N4 probed tip by using atomic force microscope (AFM). RESULTS The anti-NMDAr1 polycolonal IgG has a characteristic structure described as an ellipse spherical shape of 136.4 A x 62.8 A x 26.1 A. On the section of the ellipse edge there were two peaks about 13 nm in width. CONCLUSIONS Using AFM to investigate biomacromolecule can make us deeply understand the structure of IgG, which will instruct us to detect the membrane receptor protein as a labelling agent.