Phase behaviors of two homologous binary systems of 4-alkyl-4′-cyanobiphenyl (nCB, n being the number of carbon atoms in the alkyl chain) and 4-alkoxy-4′-cyanobiphenyl (nOCB) were investigated. Their phase diagrams were drawn against an averaged chain length, n*. The phase boundary curves between neamtic (N) and smectic Ad (SmAd) phases in nCB/mCB (n = 3-6; m = 8, 9) binary systems were classified into four depending on four combinations of even- and odd-numbered n and m; even/even, odd/even, even/odd, and odd/odd. The similar odd-even effect was confirmed for nOCB/mOCB (n = 5, 6; m = 8, 9) binary systems. To elucidate the odd-even effect on the phase diagrams, the SmAd structures were investigated through an analysis of n (n*) dependence of the layer spacing of the SmAd structure, dSmAd, of neat nCB (n = 8-10), neat nOCB (n = 8-10), and nCB/8CB (n = 0-7) binary mixtures. The odd-even effect, the behavior of 0CB/8CB system, and the difference between nCB and nOCB were clarified based on their SmAd structures. [ABSTRACT FROM AUTHOR]