4, 5-Diphenyl-2-ethoxypyrimidine (1), 3, 4-diphenyl-6-ethoxypyridazine (2) and 2, 3-diphenyl-5-ethoxypyrazine (3) were evaluated for inhibitory activity towards arachidonic acid-induced aggregation of rabbit blood platelet in vitro. 2, 3-Diphenyl-5-ethoxypyrazine (3) exhibited significant inhibitory activity. Thus, various 5-substituted 2, 3-bis(4-methoxyphenyl)pyrazines were synthesized by the nucleophilic substitution reaction of 5-chloro-2, 3-bis(4-methoxyphenyl)pyrazine (9). In a similar manner, substituted 2, 3-bis(4-methoxyphenyl)pyridines were prepared from 2, 3-bis(4-methoxyphenyl)-6-methylsulfonylpyridine (17), which was synthesized by the cycloaddition retro Diels-Alder reaction of 5, 6-bis(4-methoxyphenyl)-3-methylsulfonyl-1, 2, 4-triazine (16) with norbornadiene. Among the compounds prepared, 6-isopropoxy-2, 3-bis(4-methoxyphenyl)-pyrazine (10f) showed the most potent inhibitory activity, which was more than the activity of anitrazafen[5, 6-bis(4-methoxyphenyl)-3-methyl-1, 2, 4-triazine].