On the basis of the previous findings, relationship between the structure and sweet taste was examined by modification of the ethylene unit (B moiety) of β-(3-hydroxy-4-methoxyphenyl) ethylbenzene (1), by application of the theory of bioisosterism : N-Benzyl-3-hydroxy-4-methoxyaniline (2), 3-hydroxy-4-methoxybenzyl phenyl sulfide (4), and phenyl 3-hydroxy-4-methoxythiobenzoate (5) were synthesized. The synthesis of 3-hydroxy-4-methoxybenzyl benzoate (7) was attempted to clarify the effect of elimination of the methylene in 4-position of 8-desoxyphyllodulcin on sweet taste. As modification of 8-desoxyphyllodulcin, related lactone and lactam derivatives were synthesized. 1) Lactone derivatives ; 2-(3-hydroxy-4-methoxyphenyl)-1, 3-benzodioxan-4-one (8), and 2-(3-hydroxy-4-methoxyphenyl)-1, 3-benzothioxan-4-one (9). 2) Lactam derivatives ; 2 (3-hydroxy-4-methoxyphenyl)-2, 3-dihydroisocarbostyril (10), 2-(3-hydroxy-4-methoxyphenyl)-2, 3-dihydro-1, 3-benzoxazin-4-one (11), 2-(3-hydroxy-4-methoxyphenyl)-2, 3-dihydro-1, 3-benzothiazin-4-one (12), 2-(3-hydroxy-4-methoxyphenyl)-4-(3H)-1, 2-dihydroquinazolinone (13), and 2-(3-hydroxy-4-methoxyphenyl) isocarbostyril (14). Additionally, a lactam derivative related to phyllodulcin ; 8-hydroxy-3-(3-hydroxy-4-methoxyphenyl)-3, 4-dihydroisocarbostyril (15), was synthesized in order to examine the effect of a hydroxyl group in 8-position on sweet taste. The compounds 2, 4, 8, and 9 had a strong sweet taste, and the compound 15 had a faint sweet taste ; while the compounds 5, 7, 10, 11, 12, 13, and 14 were all tasteless. Based on these facts, the delicate relationship between the molecular structure and sweet taste was discussed.