Langmuir-Blodgett (LB) films of surface-active azodye, YOPE, were prepared at different surface pressures and observed by atomic force microscopy. The surface structure was compared with that of LB films of the arachidic acid/YOPE hybrid. The two-dimensional phase separation was observed in hybrid LB films. The molecular arrangement of YOPE on Langmuir films was inferred from the AFM observation of LB films and the surface pressure-area (pi-A) isotherms. At lower surface pressures, the dye chromophores of YOPE molecules were lying along the air-water interface. The arithmetic additivity of pi-A isotherms was substantiated for hybrids.