The phase transition behavior and layer structure of 4-octyloxyphenyl 4-(4-alkoxy-3-X-benzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-alkoxy-3-X-benzoates (X = H or NO2) were examined by thermal, microscopic, and small-angle X-ray diffraction measurements. The homologs of the former (X = H) exhibit nematic, smectic A, and Smectic C (Sm A and C, respectively) phases, and the layer spacing shows a notable change near the Sm C-Sm A transition point, while in contrast the layer spacing for the homologs (X = NO2) is almost independent of the phase transition and temperature. For the homologs of the latter (X = H and NO2), on the other hand, the layer spacing is fairly narrow compared with the calculated molecular length, and it remains constant through the Sm A and Sm C phases. These results are discussed in terms of the layer structure of the Sm A and Sm C phases, and the molecular properties are obtained by a semi empirical molecular orbital calculation.