The molecular orientations of home Y-type LB films of main-chain accordion polymer having different alkyl chain (R = 12 and 16) are investigated. The home Y-type LB films were prepared by using Miyata-type deposition system. The nonlinear optical coefficients of d33 for R = 12 and R = 16, from the result of reflected SHG intensity, are 12.0 and 8.6 pm/V. respectively. The bilayer spacing of homo Y-type LB films value from the result of wide angle X-ray diffraction (WAXD) spectra is shorter than the fully extended length of each molecule by CPK model. From the Maker-fringe for Y-type LB films, the SHG strength became the strongest when the P-P polarization was greatly slanted in the substrate. These results reveal that spontaneous polarization remains along the thickness direction. We proposed the structure of a new home Y-type LB film which is different arrangement between odd-numbered layer and even-numbered layer.