Heterostructured Langmuir-Blodgett films of stearic acid (C18) and unpolymerized pentacosadi-10,12-ynoic acid (CH3(CH2)IIC=C-C=C(CH2)8COOH) were prepared and the structures of unpolymerized and photopolymerized films were investigated by X-ray diffraction. The structural changes caused by photopolymerization were discussed. The order of deposition was varied systematically. It is found that the interplanar spacings and molecular alignments of the heterostructured films strongly depend on the order of deposition. For the three and four-layer cyclic films, a "partially overturned" structure was observed in some unpolymerized films, which means that some molecules become Z or X films from Y type. Moreover, polymerized films returned to a Y-type structure. From the films with rather thick periodicity as long as about 200 angstrom, satellite reflections were observed suggesting that high stacking order can be achieved over large distances and the macroscopic molecular orientations are highly ordered in spite of the microscopic inhomogeneity.