Self-organized domains in ring pattern of a samarium complex bounded by a beta -diketone ligand TTA-Sm(TTA)(3)Phen (TTA denotes thenoyltrifluoroacetone; Phen denotes 1,10-phenanthroline) were assembled by the Langmuir-Blodgett (LB) film technique. The domain pattern was observed by Brewster angle microscopy (BAM) at the air/liquid interface and by atomic force microscopy (AFM) on mica. A scheme is proposed for the ring domain formation on considering components in aqueous subphase and the structure of samarium complexes. The subphase containing the samarium complex and the ligands; is a fundamental condition for the stable existence of this samarium complex at the air/liquid interface. Stearic acid (SA) was mixed with the samarium complex, which formed highly ordered round domains producing a gradient electric field. Sm(TTA)(3)Phen molecules move towards and nucleate at the edge of the SA domains under electrostatic forces, resulting in the formation of a ring domain.