Abstract: The progress in scanning tunneling microscopy(STM) studies of two-dimensional magnetic structures is discussed briefly. Two-dimensional magnetic structures can be formed in the clean surface of a magnetic single crystal, or in a magnetic monolayer epitaxially grown on a nonmagnetic single crystal. A magnetic STM tip is used as probe to detect the spin-polarization structure in the surface layer. An understanding of the properties of nanoscale magnetism will stimulate the development of spintronics.