The molecular orientation of an oxacyanine dye (DOOC) in an LB film has been determined based on the second harmonic generation (SHG) using a fs-pulsed Ti-sapphire laser and the polarization absorption spectrometry. Both polarization and wavelength dependence of SHG varied with surface concentration of the dye. The dye was either in a monomer, a dimer or a J-aggregate form depending on the surface concentration. The tilt angle to the surface normal was 34 degrees for the monomer, 26-29 degrees for the dimer and 16-23 degrees for the J-aggregate. The J-aggregate stayed more flat on surface and showed larger SHG intensity than the monomer did.