Photoinduced optical anisotropy in Y type interleaving hemicyanine/arachidic acid Langmuir Blodgett multilayers has been investigated by optical linear and nonlinear measurements. Under illumination of a polarized UV nanosecond laser beam, the hemicyanine molecules would reorient and align their chromophore axes along the direction of the UV beam polarization. Thermal isotropic process was accompanied by dissociation of the H aggregate in the hemicyanine LB multilayers.