Abstract: The surface pressure-area per molecule isotherm of Gemini surfactant, propdiyl-1,3-bis (dimethyloctadecylammonium bromide)-PBDOAB, was measured at an air/liquid interface of 1.0 mol/L aqueous NaBr solution and pH=10.86. Variation of domain morphologies formed by Gemini surfactant with surface pressures at the air/liquid was observed via home-built Brewster angle microscope (BAM). (Results) show that Gemini surfactant PBDOAB forms condensed monolayer at interface and that the concentric tori can be observed at lower surface pressures, while these structures can coalesce mutually and form (multi-)centered structures, as surface pressures increase.